The baby is the fifth victim after police believe suspect, Shane Killian, 54, shot and killed four other family members in Alameda last Wednesday.
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RELATED: Alameda man accused of killing 4 family members has criminal record, spent 60 days in jail
Alameda man accused of killing 4 family members has criminal record
They believe Kilian killed his wife, father-in-law, mother-in-law, and his 6-year-old son.
The 1-year-old baby was critically injured before succumbing to his injuries.
The domestic mass shooting happened at the 400 block of Kitty Hawk Road in Alameda.
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Killian briefly appeared in court on July 12 and has a criminal past.
He served 60 days in jail for misdemeanor assault on a government official in North Carolina 13 years ago. The incident involved a gun at a gas station, which led to a high-speed chase.
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The motive is still under investigation.
Killian is expected to be arraigned in court on July 22.