Authorities in Alameda, California, identified the alleged shooter as 54-year-old Shane Killian. Facebook

A California father accused in the mass murders of his 6-year-old son, wife and in-laws was arrested Wednesday in a horrific tragedy police described as "the actions of a coward."

Authorities in Alameda, California, identified the alleged shooter as 54-year-old Shane Killian, according to KTVU-TV.

Killian was arrested at the murder scene, where the bodies of his 6-year-old son, William; wife, Nathalie Killian; and mother-in-law were recovered, said police.

Killian's father-in-law ran to a neighbor's for help, but later died from his injuries.

"These are the actions of a coward," Alameda Police Chief Nishant Joshi condemned at a press conference following the deadly incident.

Joshi said Killian's 1-year-old son, Wesley, was also shot and remains in critical condition.

A motive remains under investigation.

Killian faces several charges, including first-degree murder and child abuse, jail records indicate.

It's unclear if he entered pleas or retained an attorney to comment on his behalf.

Killian remains held without bail.