Investigators have been searching the residence of an ex-Marine who smashed a pickup truck into a Church of Jesus Christ of Latter-day Saints church in Michigan.

He opened fire and set the building ablaze during a crowded service on Sunday. He was fatally shot by police.

At least four people were killed and eight wounded.

The local police chief said “some” people were still unaccounted for. Authorities have been searching for them in the building ruins.

Authorities identified the shooter as 40 year old Thomas Jacob Sanford of a neighboring small town of Burton. The FBI said it was an “act of targeted violence”.

The attacker’s motive remains unclear. Authorities have not provided any additional details about Sanford including whether he was a member of the Mormon Church.

It was the second mass shooting in the U.S. in less than 24 hours. On Saturday night, a man in a boat opened fire on a crowd in Southport, North Carolina, killing three and injuring five.

In a social media post the US president said “this epidemic of violence in our country must end”.