After three months of investigation, police have learned more about Las Vegas gunman Stephen Paddock.

The high-stakes gambler was on a losing streak, obsessed with cleanliness, possibly bipolar and was having difficulties with his live-in girlfriend.

But hundreds of interviews and thousands of pieces of evidence have not answered the key question: Why did Paddock open fire from his high-rise hotel suite, killing 58 people and injuring more than 800 others in the deadliest shooting in modern U.S. history?

On Friday, Clark County Sheriff Joe Lombardo released a preliminary report on the Oct. 1 attack on an outdoor concert staged from a room at the Mandalay Bay casino-hotel.

He said he did not expect criminal charges to be filed against Paddock's girlfriend, Marilou Danley. She had been called the only person of interest in the case.