Police and prosecutors believe it was Rayvion Trebor Brooks, 18, who fired the shot that killed another St. Paul teenager who was picnicking at Indian Mounds Park in St. Paul on the evening of April 17.

The criminal complaint against Brooks was amended Tuesday to include four counts of second-degree murder; he and three other men already had been charged with first- and third-degree riot and committing a crime for the benefit of a gang in connection with the melee. Brooks appeared in Ramsey County District Court on Wednesday; he pleaded not guilty, and his bail was increased to $500,000.

According to the complaint, Brooks’ girlfriend told police that she and Brooks were at the park when five men “she knew to be gang members” approached them. The girlfriend said Brooks was a member of the Forever After Money (FAM) gang, and the men accused Brooks of stealing their gang’s name. Glen Dale Acon, 32, a co-defendant, told police that he gave Brooks a .357 SIG handgun after the commotion erupted.

Although Acon said he didn’t see Brooks fire the gun, it had been loaded with seven or eight bullets and was empty when Brooks returned it to him.

Another person interviewed by police said Brooks showed up at his house about 8 p.m. that night and told him that he’d just shot someone in a “crowd … 50 people deep” after the group tried to jump him, the complaint said.

In an interview with police, Brooks denied having a gun and denied firing any shots. Police found shell casings and bullet fragments from at least four different handguns that were fired that night.