CAMBRIDGE -- A Cambridge mechanic says Boston Marathon bombing suspect Dzhokhar Tsarnaev was in his shop on Tuesday, visibly nervous.

Gilberto Junior, a Cambridge mechanic who owns Junior’s Auto Body, said Tsarnaev had dropped off a white Mercedes to have a bumper and body panel repaired. Junior had planned to start the job on Wednesday, but the suspect came into the shop on Tuesday.

“He said 'I want the car right now',” Junior said. “We said we didn’t start work on the car yet. He said 'I don’t care, I don’t care, I need the car right now'.”

“I noticed he was biting his nails, looked very shaky,” Junior said. “I thought he was on drugs.”

Junior said he spoke to the FBI this morning, adding that he felt mad, sad and guilty about the subsequent violence that left MIT police officer Sean Collier dead and MBTA officer Richard Donohue wounded.

Asked why he felt guilty, Junior explained that he didn't know Tsarnaev might be involved in the bombing when the suspect visited the shop Tuesday. "He was next to me, like you are now," he said. "If I knew, I'd have knocked him down on the ground. That was the moment I could do it."

Officials on Friday said Tsarnaev and an older brother, Tamerlan, are the two bombing suspects shown in photos and videos released Thursday.

Tamerlan was reportedly killed in a confrontation with police Thursday night as officials attempted to apprehend the two brothers.