Sandy Hook gunman Adam Lanza, 20, deliberately destroyed his computer’s hard drive, erasing potentially valuable evidence, before going on Friday’s bloody rampage.

The FBI is trying to recover information from his hard drive, but has admitted it may not be possible as Lanza smashed it with a hammer or screwdriver and may also have overwritten it in a bid to hide his secrets.

Cellphones and computer games have also been seized, but police have found no evidence to suggest that he was being treated with any drugs prescribed for mental illness.

‘The kid knew what he was doing,’ a law enforcement source told New York magazine. ‘This was a planned event. There is no question about it.’

Lanza left no note or letter offering a motive for the killings, or explanation for why he targeted innocent school children.

Investigators have trawled Lanza’s home for any hope of evidence which might lead to a greater understanding of what prompted his rampage.

Connecticut State Police Lieutenant Paul Vance said investigators are examining ‘anything that can provide us with information’ about Lanza. Detectives are poring through his cellphone records and voicemails, viewing text messages and social network pages, hoping to find answers.

They are also using search warrants to get medical records to determine if he was being treated for a medical or psychiatric ailment, and what, if anything, was prescribed, a source told Seattle PI.

Much of the evidence seized involves video and internet gaming material. According to a plumber who worked at the home in Newtown, Adam Lanza was ‘obsessed’ with weapons and violent video games such as Call of Duty.

According to a plumber who worked at the home in Newtown, Adam Lanza was ‘obsessed’ with weapons and violent video games such as Call of Duty.

Peter Wlasuk, 45, said the windowless basement, where Lanza’s older brother had lived previously, was all but self-contained with computers, a TV, a bed, and a bathroom.

The walls of the room, where he spent all his time, were covered with posters of guns and tanks from as early as the 1940s and another showed every piece of equipment ever made by the U.S.

Mr Wlasuk said: ‘The kids who play these games know all about [guns]. I’m not blaming the games for what happened. But they see a picture of a historical gun and say, “I’ve used that on Call of Duty”.’

Lanza’s parents told friends and divorce mediators that their son suffered from Asperger’s syndrome, a form of high-functioning autism, but it is unclear if he was ever formally diagnosed.

All of this information could be critical to determining what caused Lanza to shoot his mom, Nancy Lanza, 52, four times in the head before then driving to Sandy Hook school and carrying out his horrific murder spree.

Using a semiautomatic assault rifle registered to his mother, Lanza brutally murdered 20 first graders and six school employees. Some were hit 11 times.

The home on Yogananda Street shared by Nancy and Adam Lanza and Sandy Hook Elementary School are being treated as guarded crime scenes for the foreseeable future.

Preston Waters | Elite.