Chris Watts' hand signals in interrogation interview caused agent to believe he may have strangled his wife

Killer Chris Watts is serving a life sentence for the 2018 murders of his wife Shanann, who was 15 weeks pregnant, and their daughters Bella Marie, four, and Celeste, three.

The killer was documented in Netflix's hugely popular true crime documentary American Murder: The Family Next Door, which featured interviews and police footage from the investigation.

And it turns out that his hand signals during an interrogation interview is what caused an agent to believe he may have strangled his wife.

Watch below:

Resurfacing on Reddit, the clip from interrogation included an explainer by agent Tammy Lee, who said that Watts made a lot of 'movements towards his neck area'. She explained: "Chris, while he was talking to Special Agent Coder made a lot of movements towards his neck area."

The clip also showed Watts move his hands towards his neck, while resting his left arm against the left side of his throat in various positions.

Netflix

Tammy concluded: "Special Agent Coder actually came out of the room and said 'He may have strangled her'."

The first sign of being guilty was also apparently evident in police body cam footage, as officers scoured his property for clues.

Body language expert Dr Cliff Lansley said: "We've got the swaying, we have the double-handed hand shrug, and we have a volume drop.

"The swaying shows anxiety, so there's anxiety going on.

"He's making an affirmative claim that she was still here when I was here at 5:15am, but his hands are doing a partial gesture...

"So that small movement of the hands, the rotation, is what we call a double-handed shrug, which is part of the full gesture [of] 'I have no confidence in what I've just said'."

Watts' shiftiness increased further when neighbours showed police CCTV footage of him loading his truck with 'work equipment' - this later transpired to be the body of Shanann.

Netflix

Dr Lansley says: "We also see a gesture which is often linked to despair or anguish, in terms of covering the head with the hands.

"If you look at Watts' face in more detail with a close-up, on the left-hand side you'll see baseline. This is Watts' normal face during the non-emotional parts of the interview.

"But on the right, when he says, 'I just want them back,' and he's talking about his children here, you see the lip corners raised. You see the eyes tighten. His cheeks are raised. This combination of these two muscles is an indicator of genuine pleasure."

Watts was sentenced to five life sentences without the possibility of parole.