ABC recounted,

In 2007, Virginia Tech shooter Cho Seung Hui removed the hard drive of his computer and disposed of his cell phone shortly before the massacre. Authorities even searched a pond for the missing digital media, but the devices were never recovered.

The 2008 Northern Illinois shooter, Steven Kazmierczak, removed the SIM card from his phone and the hard drive from his laptop, and neither was recovered.

In 2012, Sandy Hook shooter Adam Lanza had removed the hard drive from his computer and smashed it with a hammer or screwdriver.