Luigi Mangione's body language as he was escorted into a Pennsylvania courthouse gives insight into the accused killer's mindset, according to a body language expert.

Mangione, accused of killing UnitedHealthcare CEO Brian Thompson in Manhattan, was arrested in Altoona, Pennsylvania, on Monday when a McDonald's customer saw he resembled images of the suspect in the shooting. 

Charged in Pennsylvania with forgery and carrying a firearm without a license, he has not waived his right to an extradition hearing to face murder charges in New York. 

As he was escorted into Blair County Court on Tuesday by a cadre of officers, the jumpsuit-clad 26-year-old was wide-eyed and had his head on a swivel as he shouted at surrounding reporters. Susan Constantine told Fox News Digital that Mangione showed a "rigidity" that indicated he was fearful. 

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But through that, Mangione showed "a sense of arrogance and pompousness" through "just a slight raise of [his] chin" and the way that he literally looked down his nose at his surroundings. 

"Keep in mind what we're dealing with – a person who has been wronged in his own mind in some sort of way… We don't know yet exactly all the reasons why," she said. "We also know he's adopted some sort of radical belief system, and he also feels that he is the one that needs to act."

Likewise, Constantine said Mangione's chin is pointed up in his mugshot photos – both the ones taken in his orange jumpsuit and the one taken in a blue suicide prevention smock. 

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"Remember I told you that chin is up – when we see the chin up, we can see the Adam's apple pop out… the Adam's apple pops up…his nose pops up in the air," she said. "All of this is pride and arrogance and pompousness – militant and prideful."

His expression, she said, is a stark contrast from the smiling photograph of the suspect flirting with a hostel employee in New York before the Dec. 4 assassination. 

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"This was not the sinister killing [face] – this was him, his charismatic personality, his flirty personality, the one that everybody and his friends and family are all talking about," Constantine said. "He's a great guy. They like him. He's, you know, engaging and he's, you know, speaks in front of the public and doesn't have any fear about it. That's his personality."

"These types of killers disassociate – it's called cubing," Constantine continued. "So when they're in active pursuit, there is one personality. And then when he's in relationships, he has another one… he's able to disassociate from what is the sinister thoughts and ideas and radicalism that's actually flooding through his mind.

"All of a sudden, that smile turned to a frown [during his perp walk] – the lifted cheeks turn into droopy cheeks. And then he had a more rigid and more tension in his facial expression that was dissimilar to what we have seen in the past. So this was a game over expression."

The suspect's confident stance during the shooting, captured on surveillance footage, is another side to the "cube" – and indicates the planning that went into the attack. 

"He had already rehearsed – he was ready for the engagement. This was not something that just happened spontaneously. This is something that he thought out, measured and planned," Constantine said. "That's why you see his body language being very much in control. He's not startled. He knows exactly what he's going to do. That's why his countenance is down. His energy level is down because he's in hyper-focus."

Constantine told Fox News Digital that Mangione's body language – both during his perp walk and in a photograph snapped by police in a holding cell the day before – indicated that he did not expect to be apprehended by police. 

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"There are behavioral signatures and cognitions of people that are being deceptive," Constantine said. "[People display] rigidity when [they are] caught. What do they do? They sit up straight, they're very militant… So when you think about his structure, he's just very robotic."