A GoFundMe page set up to help Cunningham's wife and five children alleges he died trying to protect his family.
"T.J. always stood up for what was right and looked out for people who could not speak up for themselves," states the fundraising page, which raised more than $58,000 for the family in a day. "It's not a coincidence that his career path led to helping children through education as the assistant principal at Hinkley High School (in Aurora). His warm presence and generous spirit has profoundly impacted the lives of countless relatives, friends, colleagues and kids."
Cunningham was also a prominent alumnus of the University of Colorado’s Buffaloes football program.
Sheriff's Office officials said dispatchers received a 911 call around 9:20 a.m. Sunday from a woman who said she found a man lying on the ground, bleeding, at Eaglecrest High School in Centennial. CBS4 in Denver reported Sunday evening that the shooting took place at the athletic fields between the high school and the neighboring Thunder Ridge Middle School.
Two minutes later, Johnson called and said he had shot his neighbor, but was now at his own home about a half-mile from the school.
Johnson was taken into custody outside his home. The gun he said he used to kill Cunningham was found in plain sight in his car, according to an arrest affidavit in the case.
The affidavit states that neighbors and other witnesses told investigators Johnson and Cunningham, who was an assistant principal at Hinkley High School in Aurora, were involved in an ongoing parking dispute. A Sheriff's Office spokeswoman, Deborah Sherman, told CNN Cunningham texted Johnson about the issue hours before the shooting.
"It was a dispute that morning, they were texting back and forth, and then they said let's settle this at the school," Sherman said.
Cunningham’s brother told detectives he went with Cunningham to the school, where the two men planned to “box it out,” according to the affidavit. He said they got out of their respective vehicles and walked toward each other, yelling expletives and calling one another names.
Read the affidavit detailing the slaying of former Seattle Seahawk T.J. Cunningham below.
The shouting quickly turned deadly.
Johnson, who told investigators Cunningham had a bottle, shot the former football player three times, striking him in the head and chest. According to the arrest affidavit, Cunningham was taken to a hospital, where he died after being declared brain-dead Monday afternoon.
Cunningham’s brother told investigators he was unarmed when he was shot, the affidavit said.
Johnson, who CBS4 reported has a criminal history that includes assault and weapons possession charges, was being held at the Arapahoe County Jail without bond Wednesday.
"I expect him to remain in place," 18th Judicial District Attorney George Brauchler told the news station. "There isn't any amount of money on the planet Earth at this moment that could get him out of custody."
Cunningham, an Aurora native who was a receiver and defensive back at the University of Colorado at Boulder, was drafted by the Seahawks in 1996. His career as a defensive back lasted nine games, according to the team website.
According to ESPN, injuries ended Cunningham's NFL career.
Aurora Public Schools issued a statement Monday expressing the school district’s grief over Cunningham’s death.
"Our hearts are broken for Mr. Cunningham's family," the statement read, according to Denver7. "Our thoughts and prayers are with them during this tragic time."
Extra counselors are going to be on hand at Hinkley High all week to help students, faculty and staff process the loss, the statement said.
An electronic billboard in front of the school memorialized Cunningham on Tuesday.
“Forever a Thunderbird. Forever in our hearts,” the sign read.
Rick George, athletic director for the Colorado Buffaloes, said university officials were “deeply shocked and saddened” to learn of Cunningham’s death.
"He was a good family man and had a strong passion for working with young people, as evidenced by serving as an assistant high school principal," George said in a statement. "He was also a good alum, an active alum and took great pride in being a Colorado Buffalo.
“Our hearts go out to T.J.’s family on their tragic loss. We will miss him.”
Neighbors told CBS4 they were surprised Cunningham was involved in any dispute, let alone one over a parking space. Current Arizona Cardinals defensive coordinator and former Broncos head coach Vance Joseph, who was a college teammate of Cunningham's, also expressed shock that Cunningham was involved in a fatal argument.
"He was always a great person, a smart person. He got along with everyone. He was never a troublemaker," Joseph told Denver7. "I am shocked that this came to his doorstep. He was a great person with a big heart. Anyone who needed help in life, he was always there for them."