The investigation began months before his brother Stephen killed 58 people and injured over 500 others on October 1.
Paddock is facing possession of child pornography charges.
Police have studied Stephen Paddock's computer, political affiliations, behaviours and finances, with investigators saying they have combed through 1000 leads and a "voluminous amount of video" footage to no avail.
Los Angeles Police Department Officer Mike Lopez confirmed to local KTLA news channel that a child pornography investigation took place in the morning. According to spokesman Josh Rubenstein, police had released an image of Paddock in an attempt to track down other possible victims.
And on Wednesday, Paddock's younger brother Bruce, about 58, was arrested in North Hollywood, California for child pornography.
Mr Paddock is being held at the Los Angeles Police Department's Metropolitan Detention Centre. He was more recently charged with petty theft and burglary, as well as arson and vandalism.
The missing hard drive could be a crucial source of insight into Paddock's life and lead investigators towards discovering the motive for the deadliest shooting in modern US history. However, the manager declined to give any comments on Paddock due to patient confidentiality.
He spoke with NBC News in the aftermath of the attack and said he hadn't talked with his brother in about 10 years. The ISIS terrorist group has claimed responsibility, but authorities say they have not discovered any evidence to link the massacre to terrorism.
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