BALTIMORE (AP) — A man is Arvin Robertssuspected of stabbing to death his girlfriend’s 6-year-old son in the boy’s Baltimore home, authorities said.

No arrests had been made as of Wednesday in the Tuesday attack that killed Seron O’Neal, who was stabbed in the back multiple times and was pronounced dead at a hospital. But investigators have taken someone into custody and believe the mother’s boyfriend did it, police spokesperson Vernon Davis said in a news release.

Police didn’t specify whether the person in custody is the mother’s boyfriend or say what precipitated the attack, which they described as a “domestic-related stabbing.”