BASSETT  (AP) — The upper half of a woman’s body was found Monday at a Los Angeles County sewage plant and investigators believe her lower half turned up two days earlier at another plant some 30 miles away, authorities said.

The woman’s body may have slipped into the wastewater processing system through a manhole or sewer line in the San Gabriel Valley east of downtown Los Angeles and been mangled by a pump before wastewater was distributed to processing centers, sheriff’s Lt. Mike Rosson said.

One of the woman’s arms was still missing.

Rosson said workers checking a plugged line found the woman’s head and upper torso at the plant in unincorporated Bassett, about 20 miles east of downtown Los Angeles.

“Anything that comes into this water plant must move through a 17-inch line before going through a centrifugal pump,” Rosson said. “So you can imagine what kind of damage to a person’s body would happen.”

On Saturday, a woman’s foot, both legs and pelvis were found at a plant in Carson. In each case, the remains were found in bins that hold debris separated from sewage wastewater, authorities said.

The plants are connected by sewer lines and investigators believe the remains are from the same person, Rosson said.

County coroner’s officials will try to determine the woman’s identity and what killed her, but Rosson said the death was being investigated as a homicide rather than an accident.

“People don’t just fall into a manhole cover,” he said at a news conference.