An argument over pills or beer ended with one man setting fire to the other’s shirt, Butler police said.

The alleged victim suffered severe burns that needed treatment at a Pittsburgh hospital.

Police on Tuesday charged Michael G. Watt, 40, of Butler with the suspected crime that happened 11 months ago.

The delay in filing the case, investigators said, was because the victim, 52-year-old Mark Graham of Butler, only recently reported to police what occurred in October.

“We heard talk on the street about what happened,” city Detective Nathan Shulik said Wednesday, but no one wanted to say anything to police.

Graham in July finally had a change of heart.

“After several trips to the hospital (for treatment) and talking to family members,” Shulik said, “he decided to come forward.”

Graham said that he and Watt got into an argument on Oct. 20, 2015, while drinking behind the Grapevine Center on Elm Street, according to court documents.

He wasn’t certain if the disagreement started over pills or beer. But the defendant apparently was mad that Graham wouldn’t share, and at one point, threatened to set him on fire.

“Graham stated the next thing he recalls is being on fire,” a police affidavit said, “and tucking and rolling in an attempt to put out the flames.”

Another man was there and he witnessed the altercation. He, too, finally spoke to police after Graham came forward.

The man said he saw Watt pull out a lighter and ignite the back of Graham’s shirt. He described the shirt and the victim as going up in large flames.

“He was pretty badly burned,” Shulik said of Graham, who suffered burns all over his upper body, neck and arms.

A Butler Ambulance Service crew was called and took him to Butler Memorial Hospital. He was later flown by medical helicopter to Mercy Hospital.

Watt was already in the Butler County Prison on a pair of bench warrants when police arrested him in this case.

He was arraigned Tuesday on a felony charge of aggravated assault and misdemeanor charges of simple assault and reckless endangerment. Bail was set at $50,000.

Records showed that Watt is no stranger to the prison. Since 1998, he has been booked into the lockup 29 different times and spent a combined 1,846 days there.

His criminal history includes about two dozen convictions, four of them felonies.