The autistic 8-year-old boy allegedly murdered by his NYPD cop dad and his fiancée died as a result of hypothermia after he was subjected to “freezing temperatures” in the couple’s unheated garage overnight, police officials said Friday.

Michael Valva, 40, a 15-year police veteran, and his fiancée, Angela Pollina, 42, were charged Friday with second-degree murder in the Jan. 17 death of little Thomas Valva “because they engaged in conduct which created a grave risk of death to this child,” Suffolk County Police Commissioner Geraldine Hart told reporters during a press conference.

Thomas “was subjected to freezing temperatures” in the “unheated garage” of the couple’s Center Moriches, Long Island, home “overnight” when the temps outside were a bone-chilling 19 degrees, Hart said.

“We believe certainly that Thomas was kept in the garage overnight preceding his death,” the commissioner said.

Authorities responded to the home on Bittersweet Lane around 9:40 a.m. Jan. 17 after Valva reported that his son fell in the driveway while waiting for the school bus an hour earlier.

Valva told cops that his son lost consciousness after the fall and remained unconscious, according to Hart.

“When officers arrived, Michael Valva was performing CPR on his son in the basement,” Hart said.

Medics rushed the boy to Long Island Community Hospital and when he arrived there, his body temperature was just 76 degrees, according to Hart. He was pronounced dead at the hospital.

Thomas and his 6- and 10-year-old brothers lived at the home along with Pollina’s three daughters — 11-year-old twins and an 8-year-old girl, authorities said. All five have been placed in the custody of Child Protective Services.

An investigation into the death “revealed inconsistencies in timing and nature of the child’s injuries as reported by the father,” said Hart, who noted that police found that the boy was never in the driveway that morning.

Thomas suffered head and facial injuries “that were not consistent with” Valva’s account, and the medical examiner ruled the boy’s death a homicide “with a major contributing factor of hypothermia.”

Hart said investigators believe Thomas, as well as his 10-year-old brother, were subjected to punishment, including “food deprivation and exposure to extremely frigid temperatures.”

“We are still investigating the extent of the abuse and if it extended to all of the children,” Hart said.

According to Hart, police did a welfare check at the home in May 2019, but the family was not home at the time.

“This case has hit our department hard, even our most seasoned detectives,” the commissioner said.

Thomas’ biological mom and Valva’s ex-wife, Justyna Zubko-Valva, has alleged abuse of her three children at the hands of Valva.

Zubko-Valva, a corrections officer on Rikers Island, alleged in an interview with NBC New York that Michael starved the boys, beat them and locked them in the garage.