A man who has been allegedly stalking Rihanna also reportedly sent the pop star a graphic video.
Police began investigated the man, who went by the names Ralph Alexander and Alec Mercer on Twitter, after he posted a death threat and took a selfie outside the singer's Los Angeles home in April.
And a search warrant shows the police discovered the alleged stalker also sent the 27-year-old singer the 15-minute video, TMZ reports.
Police then electronically investigated the man and uncovered the masturbation video.
Rihanna has had a number of terrifying stalking incidents over the past few years.
In 2014, New York homeless man Kevin Mcglynn was arrested for delivering hand-written notes calling her a 'b****' to her SoHo apartment, as well as sending four letters to her LA home.
And in 2013, there were two separate attempted break-ins at her home in Los Angeles' Pacific Palisades.
In October of that year, a man was caught by Rihanna's security trying to climb the wall around her estate.
Just a week earlier, the home had been targeted by intruders while the singer was in Australia for her Diamonds world tour.
