A 54-year-old man has been sentenced to 15 years in prison for shooting projectiles with a slingshot onto highways in Monterey County more than 50 times in 2019 and 2020, prosecutors said Tuesday.

Charles Lafferty had pleaded guilty to 28 counts of assault with a deadly weapon and two counts of assault with a deadly weapon on a peace officer for a series of incidents between February 2019 and January 2020, according to the Monterey County District Attorney’s Office.

The California Highway Patrol was investigating the cases, many reported in the area of U.S. Highway 101 and state Highway 156, and used what the District Attorney’s Office described as a “detailed digital forensic analysis” to link Lafferty to more than 50 incidents.

Among the cases, six people reported cuts and scrapes from broken glass but most were uninjured and no crashes resulted from a vehicle being hit by a projectile.

Lafferty was arrested Jan. 22, 2020, in Nipomo in San Luis Obispo County and he admitted to shooting marbles at traffic with a slingshot, but did not give a motive for why he shot them. Investigators seized a slingshot and dozens of marbles from his vehicle when he was arrested, prosecutors said.