Las Vegas shooter acted strangely before shooting - report

Las Vegas shooter acted strangely before shooting - report
Photo credit: Supplied / Las Vegas police

Police have released a report detailing the investigation into the Las Vegas gunman who killed 58 people and himself, in the deadliest mass shooting in modern US history last year.

Stephen Paddock, 64, started acting strangely up to a year before the shooting, Clark County Sheriff Joe Lombardo said on Friday (local time).

Paddock's girlfriend Marilou Danley will not face any charges, despite being named a person of interest early in the investigation.

In a police interview Ms Danley said his demeanour had changed in the year leading up to the shooting, becoming "distant" and "no longer intimate", the report says.

She said he became a "germaphobic... having strong reactions to smell".

Ms Danley also observed him frequently looking out the windows at Mandalay Bay, the hotel overlooking the country music concert where he opened fire, during an earlier stay.

"Paddock would move from window to window looking at the site from different angles," the report said.

Paddock also kept child pornography and weapons in his room.

While no motive into the mass-murder has been established police say they are following a "person of interest".