Heilman had been driving "erratically" on his way home from a day of swimming at a Minnesota lake Monday when Le Sueur County Sheriff's investigator Todd Waldron approached him and later shot him as many as four times, according to authorities.
"This guy has got to go down," said the dead man's uncle, Patrick Heilman. "He's insane. You don't just gun someone down like that."
Heilman, 45, said that his nephew is survived by his 3-year-old son Haydin and his girlfriend of seven years. He had been driving to a friend's apartment in the small rural town of Kasota, Minn., about 80 miles southwest of Minneapolis, just before he was confronted by the officer.
"The cop got out of control and lost it. All Tyler had on were swimming trunks," said Heilman.
Kris Hoehn, one of Heilman's best friends who was with him when he was killed, told ABC News' Minnesota affiliate KSTP-TV that his friend had no idea the man confronting him was an officer and that if he had, he would never have argued with him.
The argument escalated into a brawl where the two men ended up wrestling on the ground.
According to police, Waldron approached Heilman, who had exited his vehicle, in an apartment complex parking lot.
When Heilman allegedly resisted arrest, according to police, Waldron tried to "detain" him and a physical confrontation began.
"If he would have identified himself and said, 'Hey, I'm an officer' and said, 'Hey, listen to me this is what's going on,' my friend would have stopped," said Hoehn.
Hoehn said Heilman eventually realized Waldron was an officer when he saw Waldron's badge's on his belt.
"Tyler got on top of him, seen that he had a badge finally, stepped back like this and the guy sprung up and fired three shots," Hoehn said.
According to Andy Skoogman, the spokesman for the Minnesota Bureau of Criminal Apprehension that is leading the investigation into Heilman's shooting, the young man had been violating traffic laws immediately prior to his death.
"Waldon has been in the area working on an unrelated case when he spotted Heilman's vehicle driving erratically and at times at high rates of speed," said Skoogman. "At one time the car had gone up a steep embankment."
It was not immediately clear whether Heilman had been under the influence of alcohol at the time and Skoogman said toxicology reports and an autopsy are underway.
Skoogman confirmed that no weapons had been found at the scene of the crime and that Heilman had, in fact, been wearing only shorts and no shirt when he was shot.
Waldon, a 10-year veteran of the Le Sueur County Sheriff's Office, is on paid administrative leave, a move Skoogman said is not disciplinary but entirely "normal" when it comes to officers involved in shootings.
Messages left for Waldon by ABCNews.com were not immediately returned.
Skoogman declined to comment on the department's protocol when it comes to plainclothes officers identifying themselves, but did say that Waldon had his badge clipped to his belt at the time of the incident, which lasted approximately 20 minutes.
He added that Waldon had called for backup in the form of a marked police car, but that it did not arrive until the shooting had already occurred.