Justus Howell, a 17-year-old who was shot twice in the back and killed by a police officer Saturday, was trying to steal a gun from a man who was trying to sell it, Zion (Ill.) Police said in a statement Monday evening.

The alleged seller, Tramond Peet, 18, of Lindenhurst, was in bond court Monday, facing two charges of aggravated unlawful use of a weapon, the Chicago Tribune reports. He was ordered held on $15,000 bail on Monday, according to the statement.

Peet was stopped on Saturday for a traffic violation by Lake County sheriff’s deputies, the statement said. During the stop, he allegedly told the deputies that he had met with Howell in the 2300 block of Gilead to sell him a gun, but Howell attempted to take it without paying.

A fight ensued and the gun discharged into the ground. Peet let go of the handgun when he heard police coming and saw officers running after Howell, who still had the gun, according to the statement. Peet also heard the officers give Howell commands and heard the gunshots.