As he meticulously planned the Las Vegas attack, the man responsible for the worst mass shooting in modern American history took elaborate steps to stymie the inevitable law enforcement investigation, according to federal court documents unsealed on Friday.

The F.B.I. search warrants shed new light on the degree to which the gunman, Stephen Paddock, who killed 58 people and wounded more than 500 others when he opened fire on a crowd from a hotel room in October, planned the attack and prepared for the aftermath. One of the warrants described how Mr. Paddock “destroyed or tried to hide digital media devices.”

Investigators said he used anonymous communications devices, including a prepaid cellphone, to cover his tracks and employed a “level of sophistication which is commonly found in mass casualty events.”

“Paddock planned the attack meticulously and took many methodical steps to avoid detection of his plot and to thwart the eventual law enforcement investigation that would follow,” the F.B.I. said.