KNOXVILLE, Ia. — A 45-year-old man must pay his father millions after a civil jury found him responsible for the death of his mother in 2015.

A jury decided Friday that Jason Carter must pay $10 million to the estate of his slain mother.

Shirley Carter was shot to death June 19, 2015, at her home in rural Marion County. She was 68. Nobody has been charged in her killing, though state authorities have said their investigation remains active.

Her husband, Bill Carter, 71, sued Jason last year, contending that the lawsuit was the only way he and other family members could find justice.

Bill's attorney, Mark Weinhardt, called the verdict a “welcome first step down the road” to justice for Shirley, Bill's wife of 52 years. He described $10 million as a reasonable verdict for the unusual civil case; it is the amount Bill's legal team asked for.

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Bill was thrilled by the verdict, though remained saddened for having to relive this experience, Weinhardt said. He cried as the verdict was read.

“He is resolute in his pursuit of justice and that’s why we tried this case, but it is very draining for him and his family,” Weinhardt said.

Bill thanked the jury for their hard work and attention through his attorney. Weinhardt said his team has “no illusions” that Jason Carter can pay a $10 million judgment anytime soon.

“This was never really about money,” he said.

The civil lawsuit, which has attracted national attention from NBC newsmagazine program "Dateline," was so tense that both sides asked for extra security in the courtroom.

Jurors began deliberations at 2 p.m. Friday to determine whether the younger Carter should be held financially liable for Shirley's shooting. Bill became emotional as the verdict was read after more than two hours of deliberations.

The jury heard from dozens of witnesses, including state agents and others involved in the criminal investigation, and listened to recordings of 911 calls made the day Shirley Carter died. Attorneys presented hundreds of pages of phone, bank and tax records, as well as crime scene photographs, to make their cases.

Who killed Shirley Carter?

Did Bill or Jason Carter kill Shirley?

The answer to that question, Bill's attorney said before the jury returned its verdict, was key as to whether jurors found Jason financially responsible in the killing of his mother.

During the hearing, Weinhardt argued that the evidence against Jason was overwhelming, while Jason's attorney, Alison Kanne, argued that it was almost nonexistent.

Bill's legal team described Jason as a lying man in need of money who cheated on his wife and killed his mother to work closer with his father on the farm, which Bill's attorney said would have benefited Jason financially. He also sought the millions of dollars in his parents' net worth, Weinhardt said, arguing that Jason may have also wanted to kill his father that day.

"Shirley's killer is in this room," Weinhardt told jurors during closing arguments before Judge Martha Mertz after a two-week trial. "This case is about a son who killed his own mother."

Kanne, however, contended that Jason had no reason to kill his mother, someone she said he loved dearly. Rather, Kanne told the jury, Bill killed his wife, arguing he benefited financially from murdering her as the executor of her will.

"Who benefited from the death of Shirley Carter? It sure isn't Jason," Kanne said. "The only person who profited was Bill."

Jason's defense team had told the jury that Shirley wanted to leave Bill. Kanne described the elderly Carter as a controlling man who killed his wife one day when he became angry. Why did he start his own investigation before police could determine who killed his wife? Kanne asked. Because he wanted to tell people who killed his wife before authorities could realize he carried out the killing, she said.

"Why hasn't Jason Carter been charged? Why aren't prosecutors sitting at that table instead of Jason Carter?" Kanne asked. "Jason Carter is innocent."

Before the verdict was returned, both sides said it could serve a statement of justice: For Bill, a liable verdict would be justice for his murdered wife. For Jason, a not-liable verdict would be justice in clearing his reputation, which his attorney argued has been smeared.

'I need an ambulance fast'

On the morning Shirley died, she and Bill went to get coffee at 7:30 a.m. at a nearby Casey's. He then drove a semi load of grain to Eddyville. Shirley had some chores to tend to, which included feeding show pigs for a grandson, Bill told police.

When Jason arrived at the home, he told authorities, he was preparing for a delivery of chemicals to spray on nearby fields. He decided to get a sandwich from his mother while he waited. The back door of the home was unlocked, which was not unusual, Jason said. That's when he found his dead mother, cold and stiff, he told police. Her body was in a pool of blood and her arms were folded across her chest.

"It was like a nightmare," he would later tell criminal investigators.

Jason called family members and talked with his sister, Jana Lain, who told him to call police. He did, and then called his father.

On the phone with 911, Jason told a dispatcher he discovered his mother's lifeless body on the tile kitchen floor in the one-story, wood-framed home.

"911 where is your emergency?" the dispatcher asked.

"Yeah, I, I need a, I need an ambulance fast," Jason Carter responded, according to a transcript of the call.

On at least four occasions, Jason said he did not know what happened to his mother.

"She's lying in a pool of blood," he said. "I don't get it."

Shirley Carter died from two gunshot wounds from a medium-caliber rifle, investigators determined. One struck her chest and the other ripped through the right side of her back, according to her autopsy report. The bullets pierced her heart, lungs, sternum and multiple ribs. A third bullet hit the refrigerator.

Bill’s legal team said Jason shot and killed Shirley from about 10 feet away, as he hid behind a barrier near the back door of the home. After he killed her, Bill’s attorneys told the jury, he picked up the shell casings so his weapon could not be identified. The rifle has never been recovered by police.

“The way this killing happened was cold,” Weinhardt said in court.

Bill Carter has repeatedly said that he believes the criminal investigation was severely mishandled and that better detective work would have led to his son being charged. After Shirley died, Bill tried to kill himself twice, he previously told the Register.

At first, detectives thought Shirley had interrupted a burglary and was killed by the offender, according to two forensic investigators hired by Bill's attorneys. They were tasked with reconstructing the crime scene to determine where the shots came from.

Investigators, according to the report they created, found that monetary items in the home, such as the victim's purse, prescription drugs and checks, had not been taken. Office and bedroom drawers had been pulled out and emptied elsewhere in the home, making the killing look like a burglary turned deadly.

Police suspected Bill or Jason Carter could be responsible for Shirley's death, court documents show. They both gave statements about where they were when Shirley was killed. Officials later identified Jason Carter as the prime suspect, the crime scene investigators hired by Bill's legal team determined.

During a recorded interview with investigators three days after Shirley was found dead, two agents with the Iowa Division of Criminal Investigation accused Jason Carter of killing his mother and lying to them. The questioning lasted more than six hours, making for nearly 200 pages of transcripts, as Jason denied their accusations.

"We need to get past this and we need to discuss what occurred that day, that something happened that you didn’t mean to happen," one agent said.

"Are you kiddin’ me?" Jason asked.

"We need to talk about that," the agent said.

"I walked in the door and found my mom layin’ there in a pool of blood."

"No, you didn’t, Jason."

"Yes, I did. And I’ll tell ya that till the day I die."

Investigators argued that Jason's timeline was not truthful or consistent. He had failed a polygraph examination, they said. Lies are hard to remember, one agent told him, and the truth would eat him alive. Killings, they said, are rarely random, especially in Iowa.

Swearing at times, Jason accused the agents of wasting their time grilling him instead of finding his mother's killer. He named other people who could have killed her. He said he would never harm "one hair on my mom’s head. Not one hair."

"She has worked her (expletive) off her entire life to die a miserable death by somebody that’s still out there walkin’ around with a (expletive) gun," Jason said.

"Jason, the person responsible for this is sitting right here today," an agent responded.

"No, he is not," Jason said.

When he walked in and found his mother, lying on her lifeless back, he began to bawl, knelt down and shook her by her leg, he told the agents. It was terrifying, he said. "It was like somethin' out of a damn horror show."

Near the end of the interview, Marion County Sheriff Jason Sandholdt asked Jason if he suspected if any of his family members were involved in Shirley's death. No, he said.

"Your dad and her, I mean, always good?" Sandholdt asked.

"Yeah. Yeah," Jason said. "I don’t know what happened to Mom."

Check back with the Register for updates.