A Long Island mother pleaded guilty Thursday to first-degree murder charges in the June 2019 deaths of her 2-year-old twin daughters, who were found suffocated in their car seats near a county park.

Tenia Campbell, 28, is expected to be sentenced to 20 years to life in prison when she returns to court in late January.

Police were alerted to the tragic story when the Medford woman's mother called police on June 27, 2019, saying that her daughter had threatened to kill herself and her toddlers. The 911 call led investigators on a desperate search for them because Campbell's mother refused to give up their location.

A call between Campbell's mother, police and Campbell herself was initiated and lasted nearly 12 minutes, but by the time they were able to triangulate Campbell's location — at the entrance to Montauk County Park — it was too late.

An East Hampton Police Officer spotted the van just off Montauk Highway, a few miles west of Montauk Point, around 4 p.m. -- less than 90 minutes after Campbell's mother called 911. She saw Campbell outside the van as she approached. Campbell's twin toddlers were found dead in their car seats in her minivan, which was pulled over on the side of a park entrance road under a sprawling tree. Asphyxiation was listed as their cause of death.

Prosecutors say Campbell later admitted to smothering them.

"This is such a sad and tragic case. Those two girls looked to this defendant, their mother, for protection and love. Instead, she executed them," Suffolk County District Attorney Raymond Tierney said in a statement. "The defendant has one thing those twin girls will never have again: life. But now, this defendant will get to live out the majority of her life behind bars."