Police spokesman Officer Eric Chiang said a man entered a Radio Shack store at 1799 Lombard St. in the Marina District at 2:50 p.m. on Friday, gathered a bunch of items, walked up to the register, and, claiming he had the powerful plastic explosive C-4, demanded money.
The man then fled and was arrested by officers nearby who found no C-4, Chiang said.
The 19-year-old man, whose name was not being released, was booked for robbery, according to Chiang. A second male suspect believed to be his accomplice was not found.
Police believe the robbery may be connected to a similar crime on Thursday, when a man walked into an electronics store at Market and Fifth streets at 3:45 p.m. and made a similar threat.
During that robbery, the suspect entered the store, said he wanted a laptop computer, then left, purportedly to check his ability to pay, according to police.
The man then came back in, brought several electronic items to the counter, opened his bag and said, "Put everything in the bag, I have C-4," police said.
The man indicated to the clerk "a taped, black box-shaped item," police said.
The clerk cooperated, handing over the items and an unspecified amount of money, and the man fled with another male suspect who had been standing at the door during the exchange, according to police.