Gunman Adam Lanza deliberately destroyed his hard drive to erase valuable evidence of his motive. Lanza, 20, deliberately erased potentially valuable evidence, before going on Friday's bloody rampage.

'The kid knew what he was doing,' a law enforcement source told reporters. '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.

Detectives are poring through his cellphone records and voice mails, 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.

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.

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.

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.

This horrifying event ranks as one of the five deadliest school massacres in history dating back to 1927.