NORWALK — A judge sentenced a Whittier man to 12 years in prison Wednesday for repeatedly stabbing his friend in the back with knife in an unprovoked attack last year in Whittier.

Roy Alfonso Zamora, 18, received the sentence after pleading ‘no contest’ to a count of attempted murder in connection with the Aug. 24, 2011 stabbing in the 8400 block of Milton Avenue, Los Angeles County District Attorney’s spokeswoman Shiara Davila-Morales said.

Zamora and a friend were drinking together about 8 p.m. at Evergreen Elementary School when the victim turned his back on Zamora while talking on his cell phone, Whittier police Det. Chad Hoeppner said.

“While the victim was talking on the telephone, out of nowhere, the suspect stabbed him for unknown reasons,” the detective said.

A motive in the crime remains unknown.