CASS COUNTY, Mo. -- Prosecutors have filed charges against two people in the shooting death of 35-year-old Steven Lawrence this weekend.

Cass County prosecutors have charged Christopher Sullivan with first-degree murder and his girlfriend, Monica Foust, has been charged with tampering with evidence in connection with the Sunday slaying.

According to the charges, Sullivan got into a fight with the victim's brother, Robert Lawrence, earlier in the day. Foust told prosecutors that she was driving Sullivan down Lyne Road when he fired a shot out of the truck.

"Chris said, 'I hope that was the right person,'" Foust said. She said that Sullivan told her to, "Go, go, go."

The cause of the earlier fight has not revealed. KCTV5 has learned that it did not involve the victim.

Lawrence died at Belton Research Hospital on Sunday afternoon.