Authorities on Thursday were expected to begin searching a second landfill for the body of a missing pregnant teen allegedly killed by her 18-year-old boyfriend.

Searchers have been digging through the Mid-Valley Landfill in Rialto since Monday for the remains of 17-year-old Anyssia Katherine Escamilla.

The search was brought to a standstill on Tuesday when crews found a large piece of skin.

The coroner's office later determined the skin belonged to a pig.

"It looks like someone just skinned a pig and put it in the trash," Sgt. Billy Green said.

Green said the crew is cautiously optimistic Escamilla's body will be found, noting that the effort would shift Thursday to a dump in Corona if needed.

Prosecutors say 18-year-old Jesus Avitia Jr. told police he killed Escamilla and dumped her body.

She was reported missing on May 11 when she failed to return home from school.

Avitia has pleaded not guilty to two counts of murder and was being held on $2 million bail.

Prosecutors say the murder charges against Avitia carry a special-circumstance allegation of multiple murder, but they have not decided whether to seek the death penalty, said Susan Mickey, a spokeswoman for the San Bernardino County district attorney's office.

Escamilla, of Bloomington, was three months pregnant with Avitia's baby.

She also has a 3-year-old son from another relationship.

Investigators say Avitia gave conflicting statements as to how Escamilla was killed. They're trying to determine a motive, though Avitia indicated he was unhappy that his girlfriend was carrying his child.

Priscilla Escamilla says Avitia's family didn't approve of the relationship because her daughter had a 3-year-old boy.

"They just didn't want them together and they still secretly saw each other," she told KTLA.

"I loved her so much. I just want her back," she added.

Family members say Escamilla and Avitia had been dating for about a year.