The screams rang out just before 1 p.m., rising from the yard of a small bungalow in Scarborough and ringing out through the tree-lined residential street.

It was clearly an argument, one neighbour said — a young man yelling, another man screaming “calm down,” prompting a woman to come out of the house to join them.

By the time police arrived, silence. Responding to a 911 call reporting a stabbing at a home near Lawndale and Argo Rds. Thursday, police officers and emergency personnel were met by a grisly sight.

One man was dead on the home’s driveway; the bodies of another man and a woman were found steps away, inside a small garage on the back of the home’s property.

All died from what police described as crossbow bolt injuries, and a 35-year-old man arrested soon after the bodies were discovered is believed to be behind the attacks, a police source said.

The identities of the victims and the suspect have not yet been released, but the police source said investigators believe they are related. As of late Thursday night, Toronto police had not yet announced any criminal charges.

Just two hours after the bodies were found, the bizarre case took another turn as Toronto police launched a separate, related investigation into a possible bomb threat at a condominium in downtown Toronto.

Around 3 p.m., police ordered residents to evacuate 218 Queens Quay, then called in the chemical, biological, radiological, nuclear and explosive team to investigate a suspicious package.

Toronto police Supt. Bill Neadles said late Thursday night that the package was discovered inside one of the units in the building, after police arrived to notify someone in the apartment about “some of the events that may have transpired today.”

They were sent to the unit by a call from one of investigators at the scene of the Scarborough crossbow deaths, Neadles said. He would not say who the condo unit belongs to.

Toronto police homicide Det.-Sgt. Mike Carbone told reporters police were only beginning their probe into the complex case, and had few details.

“With this being (only) a four-hour investigation, we still have a ways to go to determine what exactly happened,” Carbone said in a scrum Thursday night.

Immediately after the bodies were discovered, police cordoned off a wide area around the small bungalow, in a normally quiet neighbourhood near Kingston and Mason Rds. Residents arriving home in the afternoon were met with police tape blocking them from entering their houses, likely for hours.

Neighbours believe the home where the deaths occurred has been occupied in the last few years by a middle-aged couple.

Property records show the house was bought by Susan and William Ryan in 2010; neighbour Karen Mercado says William passed away two years ago.

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In an interview with the Star inside her home Thursday night — with a body still visible under a tarp, just outside her front window — Mercado said no one inside her home was aware of what happened until a family member went to leave for work and saw a large police presence outside.

“It’s scary this has happened right next door,” Mercado said. “I have two kids and this is usually a very quiet neighbourhood. I was raised in this house for 22 years and nothing like this has ever happened here before.”

Jerome Cruz was in his yard around 1 p.m. when he heard screaming coming from across the fence. His backyard abuts the yard where the bodies were found.

“I heard somebody screaming in anger and banging. A young man screaming. I heard another man say ‘calm down’ and a lady come from the house,” Cruz told the Star Thursday.

Ragu Sangaramoorthy, who lives in the area, said he arrived home from work to see his street taped off. His kids were in the back seat. “Oh my God, in front of where my kids play? . . . I’m scared now. These were human beings.”

Dale Lounsbury, who sells crossbows at a sporting goods store in Waterloo, Ont., and owns one himself, said they can be dangerous due to their power and accuracy. But they are not suited to firing multiple shots in quick succession, he said.

“Crossbows are not a rapid-fire instrument at all,” Lounsbury said. “I can probably fire two shots a minute, maybe three.”

Unlike guns, buying a typical crossbow does not require a licence.

In December 2010, a man fired a bolt into his father’s back at a Toronto public library branch in another crossbow incident that captured the city’s attention. In that case, Zhou Fang then crushed his 52-year-old father’s skull with a hammer.

Fang was initially charged with first-degree murder but the prosecution accepted a plea of second-degree murder after considering that he was the victim of long-term abuse at the hands of his father.

He was sentenced to life in prison in 2012.

With files from Jake Kivanc, Sammy Hudes and The Canadian Press