A man who pleaded guilty to assaulting a police officer during the deadly attack on the US Capitol has been sentenced to almost four years in prison, one of the longest yet for a defendant.

US District Judge Royce Lamberth on Monday sentenced Devlyn Thompson, who struck an officer with a baton, to 46 months in prison.

Thompson, who has been detained since pleading guilty in August, will receive credit for time already served behind bars.

Prosecutors in the District of Columbia had requested four years for Thompson, saying in a court filing that “a 48-month sentence would reflect the gravity of Thompson’s actions after having joined a violent mob at the US Capitol, while also acknowledging his exceptionally early co-operation and admission of guilt”.

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Thompson’s lawyer requested a one-year sentence, saying in a court filing that Thompson is autistic, and had a limited understanding of what was transpiring on January 6.

“Autism is not and should not be an excuse for bad behaviour, but rather, it should be considered when a person’s individual culpability and degree of social understanding is called into question,” the court filing stated.

A Florida man who hurled a fire extinguisher at police officers during Capitol riots, Robert Palmer, was last week sentenced to more than five years in prison, the longest term handed down so far for any of the more than 700 people charged in the attack.

Palmer was the second person to plead guilty to assaulting a police officer to be sentenced. Last month, Scott Fairlamb, a former New Jersey gym owner, received a sentence of 41 months in prison.

Jacob Chansley, known as the QAnon Shaman, was also sentenced last month to 41 months in prison.

-AAP