A Whittier couple accused of torturing and killing a young girl they had taken from her mother, who they allegedly forced into prostitution, pleaded not guilty to the crimes Thursday, authorities said.

Johnny Lewis Hartley, 39, and Mercy Mary Becerra, 43, face four felony counts in connection with the 2-year-old girl’s death: murder, human trafficking to commit pimping/pandering, torture and assault on a child causing death, according to the Los Angeles County District Attorney’s Office. The girl was identified as “Angelina W” in the criminal complaint.

The two were stopped by Mexican customs agents on Aug. 9, 2016, after X-ray machines detected the girl’s body in Hartley’s bag as they attempted to cross into Tijuana at the San Ysidro Land Port of Entry through a pedestrian lane, police said. Becerra allegedly ran when the pair was stopped but was detained a short time later, and both were turned over to U.S. law enforcement.

Becerra and Hartley are not the girl’s parents, officials said. She was the daughter of a woman, identified as “Amanda Z,” who the couple is accused of sexually trafficking between November 2012 and August 2016, the DA’s office said.

During that time, Becerra and Hartley “seized” the little girl, abused and killed her on or about Aug. 9, prosecutors allege. The complaint alleges that the girl’s torture spanned the period of Jan. 1 to Aug. 9, 2016.

Becerra and Hartley each face life in state prison if convicted as charged. The will return to court on March 16, according to the DA’s office.

The incident may have occurred in Whittier, according to San Diego police, who are working with the Whittier Police Department and the Los Angeles County Sheriff’s Department.