SAN MATEO (CBS SF) — A suspect was arrested after a police officer walked in on an armed robbery in progress at a convenience store in San Mateo in which the clerk was injured. An accomplice was also arrested, police said Wednesday.

San Mateo police officers were dispatched to a 7-Eleven store Tuesday at 12:45 a.m. to assist Belmont police conducting a high-risk traffic stop on a vehicle believed to involved in a robbery at the store.

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Minutes before, a Belmont police sergeant had arrived at the 7-Eleven and witnessed a masked man run from the store, past a vehicle waiting on him, and flee on foot southbound toward the surrounding apartment complexes, police said.

The Belmont PD sergeant entered the store to find the injured clerk who said he had been robbed. The sergeant then followed the vehicle which had been waiting and initiated a traffic stop. The driver, identified as 18-year-old Amber Zarate, was arrested and booked into jail on conspiracy charges, police said.

Benicio Munguia Bustamante, surveillance image from 7-Eleven, police evidence recovered (San Mateo Police Department)

Investigators determined the suspect entered the 7-Eleven at 12:30 a.m. wearing a red mask, green camo-style sweatshirt, blue jeans and red shoes, and holding a semi-automatic pistol. He forced the clerk at gunpoint to empty the registers but the clerk was only able to empty one cash drawer, so the suspect took the second cash drawer with him, police said.

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Before leaving, he ordered the clerk to lay on the ground and stomped on him, police said. The nature of the clerk’s injuries were not detailed.

The suspect saw the Belmont officer arriving and fled, running past the waiting vehicle and into the surrounding neighboring. Officers were not able to find him at the time.

After interviewing Zarate, the suspect was identified as 22-year-old Benicio Munguia Bustamante, Zarate’s boyfriend. Detectives began surveillance on his home on the 1000 block of Lakedale Ave. in Sunnyvale. Zarate was seen leaving the home with a woman identified as his mother, and he was arrested. Police said the mother told detectives that her son showed up at her home in Hayward asking for a ride home.

A search of the mother’s RV yielded a black bag containing a pistol, the stolen cash drawer, a red mask, and cash, police said. The pistol had been reported stolen out of Pleasanton. A search of Bustamante’s home in Sunnyvale was also conducted and detectives found a green camo sweatshirt and light blue jeans, police said.

Bustamante was booked on robbery, conspiracy, and weapons charges.

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The Sunnyvale Department of Public Safety told San Mateo police that Bustamante is believed responsible for at least one armed robbery committed in their city in February, and police said detectives would work with surrounding agencies to determine if Bustamante is linked to any other armed robberies.