Three people, including two boys, were killed in a home explosion Sunday afternoon in the U.S. state of Washington.

The explosion happened around 12:30 p.m. local time shortly after a case worker, who dropped the boys off for a supervised visitation, was forced out of the house in Graham, a city around 70 km south to Seattle, the police told local media.

According to The Seattle Times, police said that they believe Josh Powell, the husband of a Utah woman who has been missing since 2009, as well as their two young boys, Charlie, 7, and Braden, 5, were killed in the explosion.

The explosion is being investigated as an intentional act, said the police.

Powell has been a person of interest in his wife's disappearance and denied any role in the investigation. Last week, a judge ordered that Powell's sons remain in the custody of his missing wife's parents. The boys were removed from his custody last September after Josh Powell's father, Steve Powell, was arrested and charged for possessing child pornography.