WICHITA, Kan. (AP) — Three Wichita, Kansas, police officers were injured by a shotgun blast when they checked out a vacant home, and authorities were investigating Sunday whether it had been rigged to fire when the door opened.

Wichita Police said Sunday that “a modified, loaded shotgun” discharged as the officers entered the home around 4 p.m. Saturday. Investigators determined that no one was in the home at the time, but the homeowners had called police suspecting someone was inside after noticing that some windows were open.

Police said two officers remained hospitalized Sunday with injuries that weren’t considered life-threatening. One officer was in serious but stable condition and the other was being treated for minor injuries. A third officer who was hurt was treated at a hospital Saturday and released.

Officers surrounded the home for several hours Saturday before determining that no one was inside. Police Chief Gordon Ramsay said at a news conference Saturday evening that it wasn’t immediately clear whether the house had been booby trapped before officers arrived.

Police spokesman Officer Trevor Macy told The Wichita Eagle that investigators are trying to determine whether the shotgun had been rigged to fire when the officers entered.

“Apparently there were several modifications made to this one,” Macy said.

Officers from the FBI and the federal Bureau of Alcohol, Tobacco and Firearms are helping Wichita police investigate what happened.