LIVERMORE — A 17-year-old boy found at a grass fire with a cigarette lighter in his pocket was arrested Monday as a suspect in a string of arsons, authorities said.

A Livermore police officer spotted the teenager as firefighters put out the blaze about 2 p.m. at Elm and K streets, according to police spokesman Steve Goard. The officer, aware of eight recent arsons in the area, first noticed the lighter in the teen’s pocket and asked about it, Goard said.

“The juvenile initially denied starting the fire but admitted to being at some of the other fires,” Goard said in a news release.

He later admitted to starting all eight fires, and was arrested on suspicion of eight counts of arson. His name was not released because he is a minor. All of the blazes were grass fires lit about 150 yards apart, Goard said.