SAN FRANCISCO (AP) — San Francisco police say two men are in custody on suspicion of manufacturing and selling large quantities of explosives.

Sgt. Danielle Newman said Thursday that 47-year-old Marc Steven Ormando of Pacifica and 37-year-old Sean Patrick Gunther of San Pablo were arrested March 6. They face dozens of charges including possession of a destructive device and reckless and malicious possession in a public or private place.

Newman says the suspects were arrested following a months-long undercover operation by local and federal investigators that led to the discovery of more than 600 explosive devices inside their homes.

Ormando is being held on $2.75 million bail and Gunther is being held on $1.5 million bail. Both are due in court on Friday.

It is unclear if they have attorneys.

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