Law enforcement officers detonated a pipe bomb in downtown St. Helena Thursday afternoon and arrested two men suspected of having the explosive in a busy part of the city.

A suspicious vehicle parked behind a downtown St. Helena business led to the discovery of pipe bomb. The explosive was found by St. Helena police and turned over to the Napa County Sheriff’s Department bomb squad, which carefully detonated the bomb in a parking lot just off of Main Street.

The chain of events started in the early afternoon, when an employee of Napa Valley Vintage Home, next door to Ana’s Cantina on Main Street, noticed a red 1993 Chevrolet station wagon in her assigned parking spot in the alley behind the businesses.

The employee said she thought the three people inside the car looked suspicious, said Catalina Gonzalez, a bartender at Ana’s Cantina.

“She said she was afraid to approach them, so she just let it go,” Gonzalez said.

When the station wagon and the three people inside were still in the same spot several hours later, police were called.

St. Helena Police searched the Chevy and found an illegal weapon, described as a dirk or a dagger, and the pipe bomb. They arrested the two men inside and called in the bomb squad.

Armed in protective gear, bomb experts ignited the explosive device, sending clouds of smoke about 20 feet into the air.

“We got a call that they were going to explode the bomb outside our back door. The phone was barely hung up, when everyone heard a huge boom,” Gonzalez said. “No one had a chance to prepare for it. The customers said their beers were shaking on the bar.”

Aaron Corey, 30, of American Canyon, and Andrew Boos, 23, of Napa, were arrested on suspicion of possession of explosive material, possession of drug paraphernalia and possession of a dangerous weapon. The third passenger, a woman, was not charged.

Information as to what the suspects were doing parked in the alley behind the businesses and what they intended to do with the pipe bomb was not available on Thursday evening.

Gonzalez said she checked the alley area where the bomb was detonated.

“There are blown-up sand bags everywhere ... sand is all over the parking lot. Someone will have to clean up this mess,” she said. “I hope it won’t be me.”