Robert Wayne Lee, 40 – better known to his tens of thousands of online followers as Boopac Shakur – would often pose as a 15-year-old girl on social media to expose alleged predators.
His work has been known to lead to suspects being arrested.
Lee was believed to be on one of his hunts at around 10.30pm on Friday night when he approached a teenager at the Universal Coney Island restaurant in Pontiac and punched him, said Oakland County Sheriff’s Office.
Police said that the teenager was with a group of friends, one of whom pulled out a knife while another fired a gun at Lee.
The 40-year-old was struck by multiple bullets.
Lee was rushed to hospital where he died from his injuries.
The suspects, who remain unidentified, fled the scene but were later tracked down and arrested.
“There were 2 people at the table, 1 he was mostly focused on and talking to and became heated with was not the individual who shot him - it was the other person on the opposite side of the table,” said Oakland County Sheriff Michael Bouchard in a statement.
In the statement, police pointed to Lee’s work – and how his unsanctioned hunts sometimes led to false accusations being levelled against innocent individuals whose faces were then plastered all over social media.
“His one-man crusade has led to the arrest and criminal charges being filed against several men,” Sheriff Bouchard said. “He has also mistakenly identified someone as a sexual predator who was not.”
He added: “While we certainly understand his desire to hold child predators accountable, many times well-intentioned individuals who engaged in this don’t know the standard of evidence required for convictions and often underestimate the potential for violence confronting a suspected predator.”
Lee was infamous within his town, with many loving him for the work he did to identify predators.
Lee would typically message suspected predators under the guise of being a teenage girl to see if they would pursue him.
If they did, he would then post images that the men sent the fake teenager or photos from their social media profiles, alongside any previous convictions they had.
Among those he exposed was a former police officer, who is now facing charges, reported CNN.
On Saturday, family, friends and the local community held a candlelight vigil outside the restaurant where he was killed.
“He really cared about the community and especially the children... a lot of people looked up to him and respected him,” one attendee told Fox 2.
A GoFundMe page was set up by a relative to raise money to support his young daughter.
The page described the vigilante as a “true hometown hero” who “dedicated his life to protecting the innocence of our children from those with malicious intentions”.
According to the fundraiser, Mr Lee had exposed around 132 predators within his community.