San Ysidro

A San Diego man has been arrested in the Friday-afternoon slaying of a 12-year-old Mexican boy who was shot in the head just after he and three relatives had crossed the international border at San Ysidro, authorities said.

Leonard Paul Cuen, 21, of the 2400 block of Monument Road in San Ysidro was arrested about 7 p.m. by San Diego homicide detectives, and police said late Friday that they plan to search his home.

The shot appears to have been fired from the American side of the border, but no motive has been established, police said.

The incident occurred about 3:30 p.m. as the boy, who authorities would only identify as being from the interior of Mexico, was struck once in the head with what police said was a large-caliber bullet fired from a rifle.

A 22-year-old uncle picked up the boy’s body and carried it about 150 yards, where he made contact with Border Patrol agents. Authorities said the boy died instantly. None of the relatives have been identified.

The killing was the fifth and most recent in a bloody three-month period along the heavily traveled, 2-mile segment of the border just to the west of the giant San Ysidro port of entry. Last month, Miguel Angel Cancino Rios, a former car-wash employee and canyon vendor who was known as Tobi, was shot several times in the head and neck in an incident that friends and a witness say occurred after Cancino told several robbers to leave a group of immigrants alone.