LA HABRA, Calif. (AP) _ The dismembered remains of a missing 12-year-old boy were found encased in two chunks of concrete, and police arrested seven people for investigation of his murder.

Police said Sunday they were called to a home the day before by a man who noticed that someone had dropped a block of concrete about the size of a five-gallon paint can on his property. The man said he kicked the 200-pound block.

``There was blood oozing out of the bottom of the block onto the curb and flies orbiting about,'' police Capt. John Rees said. ``If you looked really close you see some tissue.''

About four hours later, a second concrete block containing body parts was discovered less than a half-mile away near another home in this suburb 20 miles southeast of Los Angeles, Sgt. Raymond Breur said.

Detectives believe the two chunks contained about 80 percent the body of Juan Delgado, who was last seen at school Tuesday. He was known to stay away from home for days at a time, so he wasn't reported missing until Thursday, said his mother, Marguerita Delgado.

The Orange County coroner said the boy died of asphyxiation.

The Delgados, who moved here from Guadalajara, Mexico, six years ago, did not live in the neighborhood where the body parts were found.

Rees said a ``trail of evidence'' led investigators to a home not far from where the first concrete block was found. The seven arrested, aged 20 to 38, lived on the property, police said.

Clothes, believed to be the boy's, were found in an alley within blocks of where authorities found an abandoned shopping cart believed to have been used to transport the concrete blocks.

More evidence was found in a tool shed. ``Cement bags. Plastic bags. Cutting instruments. Blood,'' Rees said, listing the items taken from the shed.

Authorities were seeking a motive.