A 20-year-old Texas woman and her 35-year-old boyfriend have been charged in connection with the death of a baby girl found last last month in a lake.

Heather Rose Kennedy and Donald Schultz were arrested early Friday morning, the Abilene Police Department said. Both have been charged with tampering with a human corpse, and Schultz has an additional charge of failing to register as a sex offender.

A fisherman found the body of the infant girl in a backpack on the shore of Lake Ft. Phantom Hill near Sea Bee Park on August 31, according to KTXS.

Court documents say Kennedy initially told police that the baby girl, named Peyton, lived with the child’s father in Idaho and had not come with her and Schutz to Abilene. But as investigators questioned her about the baby’s whereabouts, Kennedy abruptly stopped answering questions and demanded a lawyer.

Schutz told police that Peyton had lived with the couple in Abilene until her death. He said the baby girl died in her car seat while the couple was sleeping in their home, where Schultz said temperatures often topped 100 degrees.

A witness told police that the couple kept the baby girl’s body at the home for two to four days before taking her to the lake.

An autopsy determined the child was between 6 months and 10 1/2 months at the time of death, but a cause of death has not been determined, the Abilene Reporter News said.

An anonymous CrimeStoppers tip led investigators to the suspects, police said. Schultz is being held on a $510,000 bond, and Kennedy has a $350,000 bond.

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[Featured image: Heather Rose Kennedy and Donald Schultz/Abilene Police Department]