Updated at 12:15 p.m. with the jury delivering a life sentence.

A former football star at Skyline High and Texas A&M was sentenced Wednesday to life in prison for killing a Dallas man with a machete as he ran on a trail in Dallas.

Defense attorneys for Thomas Johnson had sought leniency, arguing that he's schizophrenic and was not in his right mind when he slaughtered Dave Stevens in October 2015.

Thomas Johnson was convicted of murder in the brutal slaying of Dave Stevens on Dallas' White Rock Creek Trail. (Dallas County Jail)

The Dallas County jury needed only an hour to deliver the maximum sentence, after spending just a half-hour deciding to convict Johnson a day earlier.

Prosecutors had told the jury that locking up Johnson for good was the only way to keep him medicated and the community safe — something his family said they had trouble doing when he first showed signs of mental illness.

Years before his son stood trial for murder, Robert Johnson knew something was off about him.

The happy, talkative kid he once knew would no longer speak to him but instead addressed the voices inside his head. Even so, the father was unsuccessful in finding mental treatment before his son left to play football at Texas A&M.

"I couldn't get any support," the father testified.

On Tuesday morning, the jury concluded that Johnson ambushed Stevens, 53, with a machete as he ran on White Rock Creek Trail on Oct. 12, 2015.

Dave and Patti Stevens, shown at their wedding. (Family)

Johnson, 25, confessed to the attack during his arrest. He did not testify during the trial, and his attorney did not call any witnesses to testify on his behalf after prosecutors rested their case Tuesday morning.

Doctors diagnosed Johnson with schizophrenia at some point before the attack. A doctor testified Tuesday that hallucinations commanded Johnson to commit acts. A person isn't guaranteed to behave violently because they have schizophrenia, the doctor said. Nevertheless, there was concern about Johnson's behavior in the years leading up to the murder.

He began to hear voices in his head and would speak and laugh to himself, relatives said.

"You'd think he was listening to a headset," his dad told the jury Tuesday.

Friends testified that Johnson wore winter hats during the summer and spoke obsessively about biblical characters, even referring to himself as "the messiah."

In 2012, he went missing from Texas A&M just 10 games into his freshman year as a wide receiver. His disappearance came a few days after he helped the team beat Alabama, the top team in the nation.

"Thomas took it as a sign from God that he was being spoken to. That he was chosen," defense attorney Paul Johnson told the jury.

Brenda Cradler, his aunt, said Johnson needed treatment well before the attack. He spoke often to her about the voices in his head, she testified. Others knew about his problems, but they wouldn't intervene, she said.

"All they saw was his athletic abilities," Cradler said as she wiped away tears. "And nobody would listen to him."

1 / 5Prosecutor Andrea Moseley shows Mark Stevens a wedding photo of his brother Dave and Patti Stevens on the stand during the punishment portion of Thomas Johnson's murder trial.(Vernon Bryant / Staff Photographer) 2 / 5Thomas Johnson watches as jurors make their way out of the courtroom during the second day of his murder trial at Frank Crowley Courts Building in Dallas on Tuesday.(Vernon Bryant / Staff Photographer) 3 / 5Mark Stevens said his brother Dave and sister-in-law Patti Stevens were "meant for each other," and that's why she took her own life weeks after his murder.(Vernon Bryant / Staff Photographer) 4 / 5Thomas Johnson was diagnosed with schizophrenia, and his defense is asking jurors to consider that when they sentence him.(Vernon Bryant / Staff Photographer) 5 / 5Thomas Johnson's aunt Brenda Cradler said the people who pushed him to excel at sports never helped with his mental problems. "All they saw was his athletic abilities," she testified.(Dave Martin / AP)

Johnson's attorney urged the jury to understand that his client acted under the influence of mental illness, but that didn't provide closure for the victim's family.

Dave Stevens, a GE engineer and a marathoner, often ran on the trail as part of his morning routine. Patti Stevens, his wife of 25 years, took her own life two weeks after his death.

"Those two were just, they were just meant for each other," said Mark Stevens, Dave's older brother. "That's why she's not here today. She just couldn't continue on."

Stevens told jurors the deaths of his brother and sister-in-law have taken a toll on his family.

His 89-year-old parents didn't make the flight from Michigan to Dallas to watch the trial because they're still dealing with the grief. His mother lights a candle for the couple each afternoon, he said.

He could only think of his brother when Johnson's attorney asked if he finds some solace in knowing Dave Stevens' killer has a mental illness.

"They're not here," he said, as he shook his head. "No."