An NYPD transit officer and his fiancée in Center Moriches were arrested and charged with murder in the death of his son.

Investigators say Michael Valva, 40, and Angela Pollina, 42, forced 8-year-old Thomas Valva to spend the night in their unheated garage last week when the temperature outside dropped to just 19 degrees.

At the time of his arrival at the hospital, Thomas' body temperature was 76 degrees.

The arrests were announced exactly one week after police first responded to the home on Bittersweet Lane to a report that the boy had fallen in the driveway. He was taken to a hospital where he was pronounced dead.

MORE: Family 'shocked and saddened' by death of 8-year-old boy in Center Moriches | Mother of slain 8-year-old says father was abusive for years 

Officials say the father's story was a lie.

“We have determined that Thomas was never in the driveway that morning and he suffered head and face injuries that were not consistent with the father's account,” says Suffolk Police Commissioner Geraldine Hart.

The couple lived in Center Moriches as a “Brady Bunch”-like family – Michael Valva had three boys and Angela Pollina had three girls in the home.

Police say they repeatedly subjected Thomas and his older brother to cruel forms of punishment, including food deprivation and exposure to extreme cold.

The family's former nanny says the two boys, both having autism, were often mistreated.

Suffolk County District Attorney Tim Sini said Michael Valva and Pollina “watched him die” and “showed not only any regard for his life, but they showed callousness that I certainly have never seen in my time as a prosecutor or as a police commissioner."

In court Friday, prosecutors revealed audio and video recordings with the two talking about the 8-year old. Prosecutors say Pollina said, in part, "Because he's cold, who f***ing knows? What are you doing?”

Then they say Michael Valva says, "I'm f***ing suffocating him."

Matt Tuohy, an attorney for both Michael Valva and Pollina, said his clients are innocent.

"They're just solely pointing the finger at, at both of these individuals and blaming them for a tragedy, so you know this, this is going to be a long road, it's going to be a fight," he said.

In court, a judge said the defendants are flight risks and denied them bail. Their next court appearance is Jan. 29.

Michael Valva was suspended without pay by the NYPD.

Justyna Zubko Valva, the mother to the boys, says her estranged husband subjected the children to abuse for years and that she documented her allegations on Twitter.