Sharlene Bosma is done with “what-ifs.”

She has spent enough time reliving the night of May 6, 2013, when her husband, Tim, headed out for a test drive with Dellen Millard and Mark Smich, who’d answered an online ad that the Hamilton-area father had posted, listing his used pickup truck for sale.

What if Sharlene had told Tim not to go with them? What if she’d asked the two men if she could see their drivers’ licences? Or what if she’d taken their photos?

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Open this photo in gallery Laura Babcock is shown in a Toronto Police Service handout photo. Handout/Toronto Police Service

Hypotheticals, she has learned, can be all-consuming.

And yet, one lingering “what-if” surged to the surface again on Monday, after Mr. Millard was convicted of first-degree murder in the death of his father, Wayne, in Toronto in 2012.

On the heels of his past convictions in the 2012 death of Toronto woman Laura Babcock, and in Tim Bosma’s death one year after that, Monday’s ruling confirmed Dellen Millard’s status as a serial killer – and Mr. Bosma as his third victim.

“I have fully thought about, if they had taken Laura Babcock’s disappearance seriously at the time … there could be two people still alive – maybe. Maybe,” Sharlene says.

“But what-ifs don’t change what is.”

Now 33 years old, Mr. Millard is likely to spend the rest of his life in prison.

But while applause broke out in the courtroom on Monday over Justice Maureen Forestell’s verdict, the Toronto cases have indeed highlighted mistakes that were made and clues that were initially overlooked. And questions have been raised about whether these investigative gaps by the Toronto Police Service and the Ontario Coroner’s Office might have cost both Wayne Millard and Tim Bosma their lives.

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Standing on the courthouse steps after the verdict on Monday, Toronto Police Detective Sergeant Mike Carbone – who oversaw the investigations into the homicides of Wayne Millard and Laura Babcock – stressed that investigators had learned from these investigations as they do from all investigations, and that the original detectives on those cases did “the best that they could” with the “available information” at the time.

Open this photo in gallery Dellen Millard during a police interview, Nov. 30, 2012. Handout

When Laura Babcock went missing in the summer of 2012, it was her ex-boyfriend who first sounded the alarm.

Shawn Lerner and Ms. Babcock had broken up earlier that year, but she was going through a rough patch, and in late June he put her and her dog up in a hotel and loaned her an iPad to use for apartment hunting.

They had last texted on July 1, and then she went silent. At first, he figured she was dodging him in hopes of hanging on to the iPad – but after a week, he became worried.

He talked to Ms. Babcock’s mother, and reported Laura missing to police.

But the 23-year-old woman had struggled with mental-health issues, and in recent months she had started working as an escort and was using drugs. She had fallen in and out of contact with family and friends, and was couch surfing.

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As a result, her absence was not immediately alarming to her family or to the police, who had minimal concerns about foul play. Among thousands of missing person cases, hers was classified as a “level one.”

The police figured she’d ditched her old life (and cellphone number) to work as an escort. She’d probably be home around Christmas, they told her mother.

But toward the end of July, Mr. Lerner got a copy of Laura’s cellphone bill, which showed that the last eight calls she had made, on July 2 and 3, were to Dellen Millard.

Open this photo in gallery Dellen Millard is shown in a police handout photo released as a court exhibit at his trial in Hamilton, Ont., Feb. 8, 2016. Handout

It was through Ms. Babcock that Mr. Lerner had met Mr. Millard. A wealthy playboy – the heir to an aviation dynasty – Mr. Millard held drug-fuelled house parties, and Mr. Lerner found him “sketchy.” He passed on the information to police.

They didn’t follow up with Mr. Millard, but Mr. Lerner did. On July 26, he sent Mr. Millard a text message: “I’m not looking to point a finger at anyone, but we’re concerned about Laura’s whereabouts and it looks like you were the last person to have spoken to her.”

“Heard about that,” Mr. Millard replied. “Don’t know where she is.”

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Mr. Lerner was taken aback by the blunt reply. He pushed back, pointing out that one of the calls had lasted 20 minutes.

Mr. Millard suggested they chat over coffee. When Mr. Lerner arrived the next day at a Starbucks, he found Mr. Millard outside, reading a magazine, sipping an iced drink – and claiming to be in a rush.

As for Ms. Babcock, Mr. Millard claimed she’d gotten mixed up with the wrong crowd, and that she’d called him looking for drugs. He didn’t give her any, he said. And he didn’t know where she was.

In fact, Mr. Millard and Mr. Smich had already killed her.

Mr. Millard had been cheating on his girlfriend, Christina Noudga, with Ms. Babcock – and Ms. Noudga had found out. Dellen promised Christina that he would get rid of Laura.

“First I’m going to hurt her,” he wrote to Ms. Noudga in a text message.

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“Then I’m going to make her leave.”

The promise, Ms. Noudga replied, made her feel “all warm on the inside.”

Mr. Millard enlisted the help of his friend Mark Smich, a high-school dropout and small-time drug dealer who dreamed of making it as a rapper.

Together, they killed Laura Babcock, and got rid of her body in a massive animal cremator that Mr. Millard had purchased a month earlier. On the side of the 6,000-pound machine, in bright red letters, was painted its brand name: “THE ELIMINATOR.”

Open this photo in gallery A photo of an incinerator taken by Hamilton Police was released as an exhibit at the Tim Bosma trial in Hamilton, Ont., Feb. 17, 2016. Handout

By the time Mr. Lerner confronted Mr. Millard at that Starbucks, police would later determine, the iPad he’d loaned to Ms. Babcock had already been hooked up to a computer at Mr. Millard’s house, and had been overwritten as “Mark’s iPad” by Mr. Smich. Mr. Smich even saved an offensive rap song to the tablet, describing the killing.

Police would also later find Ms. Babcock’s red duffel bag in Mr. Smich’s bedroom. He was using it to store spray-paint cans. Her name was still on the luggage tag.

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Four months after Laura Babcock disappeared, on Nov. 29, 2012, Dellen Millard’s father, Wayne, died.

It was Dellen who supposedly discovered the body, at Wayne’s house on Maple Gate Court in the Toronto neighbourhood of Etobicoke.

Wayne Millard, 71, was lying on his side in bed. His left eye had been shot out, and a Smith and Wesson .32 pistol lay on the floor below, on top of a shopping bag.

Instead of calling 911, and although his parents had been divorced for well over a decade, Mr. Millard called his mother, who lived about a half-hour away, in Kleinberg, Ont. It was only after Madeleine Burns rushed to the home that police and paramedics were summoned.

Open this photo in gallery This gun used by Dellen Millard to shoot his father, Wayne Millard. Toronto Police Service

It was suicide, Mr. Millard told police and the coroner, calmly: His father had a drinking problem, and had been stressed about the state of the family business, Millardair.

Wayne – who had taken over the business from his own father, Carl – was trying to expand the company, and saw it as a legacy for his son. But Dellen wanted no part of it. He didn’t want his father pouring their money into what he considered to be a floundering business.

Police photos were taken and video interviews were conducted with Mr. Millard and his mother. But although even the coroner acknowledged that the death appeared somewhat unusual, and even though a detective would later acknowledge that he got a “weird vibe” at the scene, the homicide unit was never brought in.

The death was ruled a suicide.

Seven months later, after Dellen Millard and Mark Smich were charged with first-degree murder in the death of Tim Bosma, Toronto detectives realized that two other murders might have been missed.

Although Laura Babcock’s body had never been found, and Wayne’s body had already been cremated, the cases were revisited.

Investigators analyzed the revolver that had been found beside Wayne Millard’s bed. Not only had the gun been purchased on the black market, they discovered, but Dellen Millard’s DNA was on the handle.

They also reviewed Mr. Millard’s alibi the night his father died. He’d told detectives back in November that he had stayed over at his friend Mark Smich’s house, in Oakville, west of Toronto. But now, when they checked with Mr. Smich’s girlfriend, she told them that Mr. Millard had left that night for a few hours to go on what he described as a “date.”

Sure enough, Mr. Millard’s cellphone data showed he had travelled from Mr. Smich’s place back to Maple Gate Court that night.

None of those dots were connected until after police in Hamilton closed in on a disturbing case of their own.

Open this photo in gallery Officer in charge of the Tim Bosma murder investigation, Det.-Sgt. Matt Kavanagh, is seen outside the John Sopinka Courthouse in Hamilton, Ont., on Feb. 3, 2016. Peter Power/THE CANADIAN PRESS

In their quest to solve the disappearance of Tim Bosma in May, 2016, they dug into the call records for the phone number that the two mystery men had used to set up that test drive. Although the police discovered that it was what’s known as a burner phone – set up under a fake name – they were able to glean from its call log that the pair had gone on a similar test drive the day before, in Toronto. Although that encounter had been brief, the Toronto seller offered up one detail about the taller of the two: He had a tattoo on his wrist that read “AMBITION.”

Hamilton Police immediately scoured their own records, and asked police services across the region to do the same. Their search led them to Dellen Millard.

Friends would later tell police that he had been bragging about his plans to steal a pickup truck, which confused them; now an aviation magnate, he could easily afford one. In addition to a hangar at the Waterloo airport, he owned two luxury homes, a condo in Toronto, and a farm near Cambridge, Ont. In the view of Andrew Michalski – who had moved in with Mr. Millard at Maple Gate Court after his father died – the only reason he had to steal a truck was for the thrill.

Open this photo in gallery Police search a farm connected to the death of Tim Bosma on horseback and on foot after human remains were found, near Kitchener, Ont., May 14, 2013. J.P. MOCZULSKI/The Globe and Mail

On May 10, four days after Tim Bosma disappeared, Mr. Millard was arrested. As he was handcuffed and led away from his SUV, the key to Mr. Bosma’s truck dangled on his keychain in the ignition.

Police found the truck, which had been stripped and gutted, hidden in a car trailer parked in Mr. Millard’s mother’s driveway. Tim Bosma’s body, it would later be discovered, had been cremated in the same incinerator that Mr. Millard and Mr. Smich had used to get rid of Laura Babcock’s body 10 months earlier.

On May 22, Mark Smich was also charged. Days earlier, after the public had learned that Mr. Bosma was dead, he’d attended his sister’s wedding, smiling for photos and giving a thumbs-up to the camera.

As police led him away in handcuffs the day he was charged, he called out to his girlfriend: “Don’t tell them anything, babe.”

Mr. Millard, too, was busy reaching out to his own girlfriend. For close to a year after his arrest, Dellen wrote letters to Christina from his jail cell, stressing the need for them to “get [their] stories straight.”

He wasn’t just talking about the Bosma case. He also outlined a detailed script for “the night Laura disappeared."

Open this photo in gallery Police execute a search warrant at a far property owned by Dellen Millard in North Dumfries, Ont., Sept. 9, 2013. Kevin Van Paassen/The Globe and Mail

“Here’s what happened,” he instructed in one letter. “Laura was over doing coke with Mark in the basement. We went to say goodnight to them. You saw her alive with Mark with coke.”

Ms. Babcock then overdosed, he coached her.

He ended each of his letters with an instruction to destroy them. But Ms. Noudga hung on to them, penning her own in response. In one, she chillingly referred to her boyfriend as her “sweet serial killer.”

On April 10, 2014, she was charged with being an accessory after the fact to Mr. Bosma’s murder. (She would plead guilty in 2016 to the lesser charge of obstructing justice by willfully destroying evidence – wiping fingerprints from Dellen’s car trailer on the day of his arrest).

When police searched her house, they found the letters.

It was that same day that police announced that Mr. Millard and Mr. Smich were now facing a second murder charge, in the death of Laura Babcock. And Mr. Millard, alone, was additionally charged with murdering his father.

One month later, Shawn Lerner filed a formal complaint with the Office of the Independent Police Review Director (OIPRD) about their handling of the Laura Babcock case.

At the time, he told The Globe and Mail, “The Toronto Police completely botched the investigation, as far as I am concerned.”

The OIPRD has since concluded that, because Ms. Babcock had been considered a “level one” missing person – meaning there were minimal concerns about her safety – the extent of the detectives’ investigation was appropriate.

The file was closed in 2015, with no finding of negligence. There is no opportunity for review. The OIPRD would not discuss the file with The Globe and Mail, citing privacy rules. When contacted by The Globe this week, Mr. Lerner declined to be interviewed.

Earlier this year, the Toronto Police Service commissioned both internal and external reviews of their handling of missing-persons cases, after alleged serial killer Bruce McArthur was charged in the deaths of eight men with ties to the city’s gay village dating back to 2010. Many people in the LGBTQ community had long raised concerns about a potential serial killer in their midst, and they say their fears – and the disappearances – were wrongly dismissed by police.

Open this photo in gallery Hamilton police Det.-Sgt. Greg Jackson, who was the case manager on the original investigation into the Tim Bosma murder, arrives at the John Sopinka Courthouse in Hamilton, Ont., on Feb. 3, 2016. Peter Power/THE CANADIAN PRESS

The review will also look at the investigations into two other missing-persons cases. One is that of Alloura Wells, a homeless, biracial and transgender woman whose body was not identified for months after she was found dead in a Toronto ravine. The other is that of Tess Richey, whose family found her body in a laneway last year, steps from where she’d last been seen in Toronto’s gay village, after police officers allegedly failed to do a proper canvas of the area.

But despite the concerns that have been raised about the handling of Laura Babcock’s disappearance, her case is not slated to part of that probe.

The Ontario Coroner’s Office produced a report this summer into “secret homicides” – cases that were mistaken as suicides, or as accidental or natural or undetermined deaths – going back decades. The report – which looked at the medical findings in those cases, not at the police investigations – was commissioned as part of the inquiry into the murders of eight senior citizens by former Ontario registered nurse Elizabeth Wettlaufer.

In all, the report looked at 17 deaths. Among them were that of Tammy Homolka, who was killed in 1990 by her sister, Karla Homolka and Karla’s fiancé, Paul Bernardo; and Bill and Bridget Harrison of Mississauga, whose murders, in 2009 and 2010, were detected only after their son Caleb was killed years later.

But at the time that the report was being produced, the Wayne Millard case was still before the courts, and therefore was not included.

When the verdict was delivered on Monday in the Wayne Millard case, Laura Babcock’s parents, Linda and Clayton, were sitting at the front of the courtroom. Tim Bosma’s parents, Mary and Hank, sat right behind them. All four applauded when the 33-year-old was found guilty.

Outside the courthouse, the two couples, bound by grief, addressed reporters.

Attending the trial each day had been torturous, Mr. Babcock said. But they needed to be there to ensure that someone there cared about Wayne, and about the outcome of the trial.

They thanked the police and the prosecutors and anyone who had come forward to help – but did not mince words for those in Mr. Millard and Mr. Smich’s inner circles.

“For all of you who knew or suspected what Millard and Smich had done to Laura, and did not come forward earlier, we again say: Shame on you,” Mr. Babcock said. “Your inactions have indirectly led to two additional murders.”

Sharlene Bosma – who goes by a different name today, one that The Globe and Mail is not sharing, for the sake of her privacy – was not there for the verdict on Monday. She decided that it wouldn’t have been best for her mental or emotional health.

Now, almost 40, she has worked hard to rebuild her life and to be happy. She has moved to a new house, and, as of just weeks ago, she is remarried.

Her new husband, Wes, was one of Tim’s closest friends. In fact, Tim was the best man at Wes’s first wedding, and Wes was a groomsman at Tim and Sharlene’s.

He was living out West during the Bosma trial. But after a difficult divorce last year, he moved back to Ontario, where he and Sharlene leaned on each other for support. Slowly, their friendship turned romantic.

On Sept. 8, after a short engagement, and after delivering notes to their neighbours to apologize for the noise, they held a backyard wedding at their new home.

Open this photo in gallery A photograph of widow Sharlene Bosma and her late husband, Tim Bosma, at a memorial in Hamilton, Ont., May 22, 2013. Nathan Denette/THE CANADIAN PRESS

Speaking to a reporter on their back porch on a recent Sunday afternoon, Sharlene and Wes spoke about how they have “helped each other heal.”

Sharlene did attend portions of the Laura Babcock trial last fall.

She wanted to make sure the two killers were given consecutive sentences, in hopes that her daughter, who is now 7, will never have to face them at a parole hearing.

She is hopeful that Mr. Millard will receive a consecutive – rather than concurrent – sentence for his father’s murder as well.

She sees value in a review of some sort by Toronto Police, and said that that would certainly be an “extra silver lining.” But it is not something she will campaign for. Justice, she feels, has been achieved. Her goal is to move forward, ensuring, now with Wes’s help, that her daughter knows how much Tim was loved, and that he is never forgotten.

“How you go on in life is a matter of perspective,” she says. “It becomes a choice about how much more you are willing to give them. And for me, I’m done."