In a Thursday update on Facebook that appeared to have been written by Jake England, 19, he angrily blamed his father's death on a black man and used a racial slur. He said Thursday was the second anniversary of his father's death.
"It's hard not to go off," given the anniversary and the death of his fiancee this year, the posting said.
"It's apparent from the posting on the Facebook page that he had an ax to grind, and that was possibly part of the motive," Willingham said.
The Facebook page had been taken down by Sunday afternoon.
A family friend, Susan Sevenstar, told the Associated Press that England was "a good kid" and "a good, hard worker," who "was not in his right mind" after losing his father and the January suicide of his fiancee, with whom he had recently had a baby.
"If anybody is trying to say this is a racial situation, they've got things confused," said Sevenstar, who described England as Cherokee Indian. "He didn't care what your color was. It wasn't a racist thing."
The Tulsa World reported that England's father, Carl, died after he was shot in the chest during a scuffle with a man who had tried to break into his daughter's apartment.
The man charged in the shooting is serving a six-year sentence on a weapons charge, according to Department of Corrections records.
Acting on an anonymous tip and backed by a helicopter, police arrested Jake England and Alvin Watts, 32, about 2 a.m. Sunday at a home in Turley, just north of Tulsa. The two men were roommates, and officers went to their home, then followed them several blocks to another home, where they were arrested without incident, police said.
Authorities said they planned to charge them with murder and other offenses. Task force commander Maj. Walter Evans, task force commander, said that investigators recovered a weapon but that it was not clear who fired the shots. They also found a truck that had been burned.
Police previously said they were looking for a man in a white truck.
Police Chief Chuck Jordan said the gunmen appeared to have chosen their victims at random. Police identified those killed as Dannaer Fields, 49, Bobby Clark, 54, and William Allen, 31. Two men were wounded but were released from the hospital, Jordan said.