Police are tracking a stalker who managed to tweet a photo of himself outside Rihanna’s former home, and also threatened to kill her with a gun.

The stalker, who goes by Alex Mercer on twitter, wrote that he should have killed her when he went to her house. Police tried to apprehend him but he was gone by the time they got there, and they’re tracking him electronically now.

From TMZ:

“Rihanna’s alleged stalker is about to have cops crawling up his cyber a$$ … searching his online accounts after RiRi got a terrifying gun threat on social media.

Law enforcement sources tell TMZ … LAPD will scour the records of someone who goes by Alex Mercer and Ralph Alexander on Twitter and Yahoo. We’re told the guy posted a selfie of himself on April 30 outside Rihanna’s former home.

The next day, he tweeted … “Should of killed @rihanna a minute back I would be good right now. Sorcery is a weapon I use guns, bout to get a gun license, can’t use my hands.”

Police went to Rihanna’s house, but he was gone by the time they arrived. So, now they’re tracking him down electronically — through phone, computer, and social media records.”