S.F. robbery bust turns up 38 guns, bomb materials, police say

San Francisco police showed off guns seized from a robbery suspect at a news conference on June 10, 2015. San Francisco police showed off guns seized from a robbery suspect at a news conference on June 10, 2015. Photo: Sfpd Photo: Sfpd Image 1 of / 3 Caption Close S.F. robbery bust turns up 38 guns, bomb materials, police say 1 / 3 Back to Gallery

After a two-month investigation into a series of San Francisco robberies, police arrested two suspects, one of whom allegedly had 38 guns, bomb-making materials and explosives at his house.

Police Chief Greg Suhr said at a news conference Wednesday that the probe resulted in “as large a seizure as I can remember going back to 2009.”

Officers reported seizing 22 assault weapons, 12 handguns, two bolt-action sniper rifles and two shotguns. A bomb-making kit and explosive devices that were found do not appear to be tied to terrorist activity, police said.

Bayview Station investigators said they believe the guns were meant to be trafficked in the area. The Bureau of Alcohol, Tobacco, Firearms and Explosives is investigating the weapons as well.

The string of four robberies occurred from April 22 to May 19, with suspects using handguns to target two gas stations in the Bayview and two stores, one on Divisadero Street and the other on Folsom Street, police said. No one was hurt.

Officers named the crime spree the “Letterman Robbery Series” because one of the suspects wore a brown and black letterman-style jacket. The men robbed at least one of the four businesses together, police said.

On May 24, officers arrested 56-year-old San Franciscan Homer Mathews, who allegedly wore the jacket, on suspicion of robbery and conspiracy to commit robbery.

Officers later spotted a car matching video surveillance from the robberies and arrested Austen Chin, 31, of South San Francisco on suspicion of robbery as well as kidnapping for allegedly forcing a store owner into his business to facilitate the heist.

Officers searched Chin’s house June 3 and found the weapons, officials said.

Jenna Lyons is a San Francisco Chronicle staff writer. E-mail: jlyons@sfchronicle.com Twitter: @JennaJourno