Carl England, whose son is accused in the weekend shooting spree, was fatally shot in 2010 by a man who had threatened his daughter and tried to kick in the door of her home.
The man was black, and police say England's son may have been seeking vengeance when he and his roommate shot five black people last week.
Police documents given to the Associated Press said the two suspects have both confessed. According to a police statement, 19-year-old Jake England admitted shooting three people and 32-year-old Alvin Watts confessed to shooting two.
Also Monday, the two suspects appeared in court to have their bond set at $9.16 million apiece. Authorities have said they expect to charge the pair with three counts of first-degree murder and other crimes.
Family and friends say Carl England's death sent his son into a downward spiral. On Thursday, Jake England apparently wrote a Facebook post marking the second anniversary of his father's death and lamented that "it's hard not to go off."
Back in 2010, Carl England had responded to his daughter's call for help and with her boyfriend tracked down the man who tried to break in. A fight broke out, and the man took out a gun and fired at England.
The man who pulled the trigger, Pernell Jefferson, was not charged with homicide because an investigation determined he acted in self-defense.
Jefferson was charged with attempted burglary and a weapons violation and had his probation revoked in an unrelated weapons case for which he is serving a six-year sentence. He is scheduled to be tried in May on the burglary charge.
According to an affidavit, Jefferson tried to kick in the door of the apartment England's daughter shared with her boyfriend after the boyfriend hit him with a baseball bat during an earlier confrontation at the couple's home.
When Carl England and the boyfriend found Jefferson, Jefferson came at England, who hit Jefferson with a stick. Jefferson fell to the ground, pulled out a handgun and fatally shot the elder England.
Jefferson fled but was arrested after seeking treatment for his injuries at a hospital.
Watts' brother, Gene, told the Tulsa World that Watts moved in with England soon after his father died to help him rebuild his life and deal with his anger, which seemed to be racially focused.
"I've never known my brother to be no racist or anything like that," Gene Watts said. "I know he was going through a little bit of depression problems, but other than that, he's got in little scuffles before, but he's never went off and done this."
Alicia Houston, who lives near the roommates, told the newspaper she has known England since he was a child and "from the time his father died, that boy has been somebody else." She said England needed therapy "from the beginning" but didn't receive it. He was taking medication for depression, she said.
The January suicide of England's fiancTe, only months after she gave birth to their son, made matters worse. Sheran Hart Wilde died from a self-inflicted gunshot to the head on Jan. 10, according to the state medical examiner's office.
All of those killed in the spree were apparently random targets who were shot while walking around.
Dannaer Fields' niece said her aunt never felt unsafe in her neighborhood.
"I can tell you she was a loving and giving person, and she had no fear of walking the streets," Deatrah Fields said. "She knew pretty much everyone. She was two blocks from her house when she was shot."
Fields had worked as a caretaker but was on disability, her niece said. Another niece said previously that she didn't have a car and was probably headed home.
Ralph Eady owns a men's clothing store across the street from where one body was discovered. When he pulled up for work Friday morning, more than a dozen police cars and a crowd of onlookers were outside his business.
Eady, who has a concealed weapons permit, said he quickly armed himself with a 9 mm handgun and a snub-nosed .38.
"Before the suspect was caught, everybody was on pins and needles," he said. "Everybody started getting locked and loaded, strapping on their guns and doing what they needed to do to defend themselves."