Sandy Hook mass killer Adam Lanza was filmed playing an arcade dance game by himself months before he shot 26 people dead and committed suicide, authorities confirmed today.

In the video Lanza, 20, can be seen playing popular arcade game Dance Dance Revolution in which players press buttons with their feet along to music - scoring points for each correct step.

The video, filmed at the AMC movie theater in Danbury, Connecticut, was first uploaded to YouTube in June 2012, but authorities only today confirmed that it shows Lanza, Newsweek reported.

Adam Lanza, the Sandy Hook school shooter who killed 26 people before committing suicide, was filmed playing arcade game Dance Dance Revolution months before the attack, authorities said (pictured)

In the footage Lanza can be seen pulling off a complicated dance routine across two of the game's dance pads, typically used for two people playing alongside one another.

A group of people filming the video can be heard talking quietly as he dances, at one point laughing, though it is not clear whether they are laughing at him.

GPS data from a tracker that Lanza was given by his mother before the shootings shows that he went to the movie theater most weekends to play the game, for between four and ten hours per day.

Lanza was known to play the game at a Connecticut movie theater for up to 30 hours each weekend in the year before he carried out the shootings

A copy of the game and a dance mat was also found inside his home, according to a 2013 police report, along with multiple videos and screenshots of him playing it.

According to an acquaintance of Lanza, who was interviewed by police, the pair used to play the game together from 2011 until June 2012, after which Lanza appears to have played alone.

The friend added that Lanza was able to endlessly play the game, not appearing winded or tired unless he became really exhausted.

Police say GPS records show that Lanza visited the theater to play the game until around a month before the shootings, at which point he stopped.

Lanza was known to spend a lot of his time playing video games, and a search of his home in 2013 revealed a basement area filled with gaming paraphernalia.

Alongside games designed for younger audiences - such as Dance Dance Revolution and several Super Mario titles - were more violent games.

Among them were multiple first-person-shooter games such as Call of Duty, Halo and Doom, alongside other violent titles such as Left 4 Dead and Grand Theft Auto.

Also included was a game called 'School Shooter', a modified version of a shooter game in which the player carries out a mass killing inside a school.

According to friends, the shooter spent most of his time playing video games, both solo and online, engaging in all-day gaming sessions.

Six months after the footage was taken Lanza killed 26 people, including 20 children an his own mother, in an attack on Sandy Hook Elementary School in Connecticut

While police discovered that Lanza owned several violent video game titles in the wake of his killings, he also owned several games aimed at younger audiences, including Dance Dance Revolution and Super Mario

As well as playing video games, the killer was known to build and repair computers, working for a time at a repair shop, as well as being interested in poetry and hiking.

He was regularly taken target shooting by his family, the report says, and while he was familiar with firearms he did not own a licence himself.

Authorities confirmed the video as the families of Lanza's victims attempt to mount a wrongful death lawsuit against the company that produced the weapon he used in the killings.