Three days after a Baton Rouge boxer was shot and critically wounded, police arrested the 21-year-old man who is a suspect in the shooting — and now say the boxer was an innocent bystander to an argument when shots rang out.

Christopher Stills was booked into Parish Prison on Thursday afternoon, less than a day after police issued a warrant for him in the Monday night shooting of Emanuel Augustus, 38.

Stills was booked on counts of attempted second-degree murder, felon in possession of a handgun and illegal use of a weapon, according to the affidavit of probable cause.

Police offered new details Thursday in the shooting, which suggest that Augustus was an innocent bystander and was shot in the head when he walked by Stills, who was arguing with another man, said Cpl. Don Coppola, a Baton Rouge police spokesman.

Stills was arguing with a cousin while his cousin was driving a red car on Louisiana Avenue just north of Government Street, the affidavit says.

The car is the same one shown in a photograph that police released early in the investigation, Coppola said.

Stills and his cousin were arguing while his cousin drove — until the fighting grew so intense that Stills’ cousin slammed on the brakes, bringing the car to a halt in the middle of the road, and Stills jumped out and began firing a gun, the affidavit says.

At the same time, Augustus, who spent over a decade as a professional boxer and had only recently moved back to the city where he had grown up, was walking by and found himself in the path of bullets that Stills fired over the top of the car, according to the affidavit.

One of those bullets struck Augustus in the head.

A man who also happened to be walking along the street witnessed the red car brake to a halt and took off running at the sound of gunshots, the affidavit says. It was only later that the witness realized he was feet from Augustus when the shooting started.

After the shooting, Stills got back in the car and the cousin drove him away. According to the affidavit, the cousin “was afraid and didn’t know if (Stills) would harm him.”

The cousin later cooperated with police, according to the affidavit.

Stills, 2515 Finch St., Baton Rouge, had been sentenced to five years probation for simple robbery and burglary charges in separate cases from 2013, court records show.

Augustus remained in critical condition on Thursday, Coppola said.

The boxer was born in Chicago but grew up in Baton Rouge and worked his way up to facing famed opponents like Micky Ward and Floyd Mayweather Jr. But in recent years, a friend convinced him to quit because the fighting had been taking a toll on his body.

After his retirement, Augustus encountered other hardships.

He left Texas about a month ago with no driver’s license or suitcase and only minimal possessions but with hopes of making a new life after his boxing career had drawn to a close, a friend said Tuesday.

Augustus was shot just blocks from the boxing gym where he first trained while growing up in the city. At the scene of the shooting, police found a pair of red boxing gloves lying in the road.

Editor’s note: This article was changed on Friday, Oct. 17, to reflect that the Baton Rouge boxer Emanuel Augustus was critically wounded, not killed in a shooting Monday night.