Apparently/allegedly he did enough advance planning to smash his computer so that police couldn't recover evidence from it
I wouldn't be too worried:
But in the age of cloud computing and multiple Internet-connected devices, authorities have no shortage of ways to follow his online footprints for clues, from acquiring his emails and search history to obtaining his online correspondence while he reportedly played "Call of Duty" on Xbox, experts said.
"Your Internet history is very telling," said Monique Ferraro, an attorney and digital forensics expert. "Even without a hard drive, if he was on the Internet, and most people are, investigators will be able to tell quite a bit about what he was doing, where he was going and what he was thinking."
And if, for example, Lanza used Google for email or Web search, law enforcement officials will likely subpoena the company to gain access to the content of his emails or what sites he visited after conducting a Google search, according to experts. As the recent email scandal involving retired Gen. David Petraeus highlighted, it's very difficult to hide the details of correspondence from law enforcement -- even for the director of the CIA.
Adam Lanza's Smashed Hard Drive Doesn't Erase His Digital Footprint, Experts Say