Former Skyline High School and Texas A&M football player Thomas Johnson remained behind bars Sunday after he admitted to randomly killing a jogger with a machete on White Rock Creek trail in Dallas.
Robert Johnson believes his son's mental illness may have driven his son to commit murder.
David Stevens, 53, of Sunnyvale, was found dead Monday, Oct. 12.
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"They have my prayers and they have my sympathy," Robert Johnson said of Stevens' family. "I wish I could turn back the hands of time, but I can't do that. I'm not God."
Robert Johnson said his son was diagnosed with schizophrenia in 2014.
"The disease itself is a monster. The disease will create havoc for anyone that comes in contact with it," said Johnson. "What murderer do you know actually hurts someone, turns around and goes to the phone and say, 'Hey, I killed a man'?"
Robert Johnson spent time with his son four days before the murder and said he has not spoken with him since.
"No matter where he is on the face of this planet, I'm going to be his dad," Robert Johnson said. "I'm going to love him unconditionally because God blessed me with him."
Thomas Johnson has prior felony convictions, but none for violent crimes.
On Jan. 9, he pleaded guilty to unauthorized use of a vehicle and to burglary of a habitation. He was sentenced to four years probation on both offenses and fines of $3,500. The Dallas County Sheriff's Department had two outstanding warrants for Thomas Johnson on the same offenses, with bond being set at $200,000.
Thomas Johnson, who grew up in Dallas, played football for Texas A&M University in College Station in 2012. In his short collegiate career, he had three catches for 22 yards in A&M's 29-24 win at top-ranked Alabama. He disappeared from College Station a few days later and wasn't seen again until he appeared at his family's Dallas home three days later. He never returned to A&M.
It's not clear if Thomas Johnson has an attorney.
A memorial run in Stevens' name is scheduled for Monday night in Dallas.
NBC 5's Frank Heinz contributed to this report.