The 15-year-old youth charged with shooting another teen in a crowded Tim Hortons this weekend used a modified flare gun, police say.

The flare gun used in the incident at 779 Barton St. E. had been altered or modified "in an attempt to discharge a projectile," Hamilton Police said in a media release on Monday.

Officers learned this after they sent the gun to the Centre of Forensic Sciences, and tests showed it was a flare gun. Now police say they're trying to determine if the modifications render the flare gun a "firearm" for the purpose of criminal charges.

Police were called to the coffee shop just before 4 p.m. on Saturday, the news release said. Witnesses said they saw someone pointing a firearm at a teenage boy and fire a shot. Both people then left the Tim Hortons.

Officers searched the area and found the victim walking in the area of Lincoln Street and Barton Street East. He had "a superficial injury that did not require immediate medical treatment," police say.

Just after 9 p.m., police arrested and charged a 15-year-old with assault with a weapon.