FOSTER CITY (CBS SF) – A man has been arrested after authorities seized illegal weapons at a Foster City home, including a machine gun with a grenade launcher.

According to the Contra Costa County Sheriff’s Office, deputies with the CASE Team arrested 41-year-old Joseph Holmes last Thursday without incident while executing a search warrant at his home on the Peninsula.

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Deputies said they were following a tip that Holmes allegedly obtained Glock conversion switches, which allow pistols to fire in full automatic mode, making them illegal machine guns.

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The seized items include four Glock conversion switches, three AR-15 assault rifles, a machine gun with attached silencer and grenade launcher, along with nearly two dozen large-capacity magazines.

Weapons seized by the Contra Costa County Sheriff's Office while executing a search warrant in Foster City on June 20, 2019. (Contra Costa County Sheriff)

Weapons seized by the Contra Costa County Sheriff’s Office while executing a search warrant in Foster City on June 20, 2019. (Contra Costa County Sheriff)

Holmes faces multiple charges, including possession of a machine gun, possession of an assault rifle, manufacturing an assault rifle, possession of a silencer, possession of a destructive device, illegal transfer of a firearm, importation of large capacity magazines and possession of an explosive agent.

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Deputies said their investigation will be forwarded to the Contra Costa District Attorney’s Office for prosecution.