Cunningham, 46, an NFL security during the 1996 season, was run by a neighbor early Sunday and taken to a hospital, where he died Monday, the sheriff office said via Twitter.
Cunningham was apparently shot during a parking dispute, but the details of the argument were not available. The shooting took place near Eaglecrest High School and Thunder Ridge Middle School in Aurora.
The neighbor, Marcus Johnson, 31, was originally held for attempted murder charges, but the charges were changed to first-degree murder after Cunningham's death, according to the Sheriff's office.
It is not clear whether Johnson, who was held without a bond, has a lawyer.
Aurora Public Schools said in a statement: "We are deeply saddened to learn that one of our assistant leaders, Anthony (TJ) Cunningham passed away."
Advisors were available at Hinkley High School, where Cunningham worked throughout the week, the statement said.
Cunningham played broad receiver and defensive back at the University of Colorado. He was the 209th overall pick in the 1
Colorado Buffaloes said on Twitter that Cunningham was "a huge part of the CU community and touched countless others beyond Boulder."
"We were deeply shocked and sad to learn about T.J.'s death. Cunningham. He was a good family member and had a strong passion for working with young people."