9:20 AM PT -- TMZ just found a video Nunn posted 10 months ago ... rambling about things "taking so long" with Kathy, but says he enjoys watching her makeup tips. Nunn refers to Kat Von D by her full first name in his tweets. He seems out of it in the video, and also rants about President Obama.
Kat Von D fears for her life and the lives of others after getting online death threats from a man who says he's planning a Columbine-style bloodbath ... and police are desperately trying to locate him.
An LAPD search warrant gives a chilling account of threats allegedly made by Michael Nunn -- an Iowa man who claims Von D destroyed his life.
On June 4 he tweeted ... "You have to understand, Kat, my life is over because of you. Therefore, what would my only reason for living be? Revenge." He added he wants people to feel guilt for "what I'm about to initiate in a few weeks" ... and threatens to "go Columbine in Los Angeles."
He also told Kat ... "Get it through your f****** head!! Lose the game or watch people die!" -- and, "Your [sic] running out of time and I'm not running out of anger and determination."
Police say Nunn and Von D have a history ... she got a restraining order against him back in 2012 after he allegedly harassed her with creepy phone calls and showed up at her home and work.
The threats sound eerily similar to the chilling video made by Santa Barbara campus shooter Elliot Rodger ... when he spoke of getting revenge.
Police say they've been unable to locate Nunn. The search warrant gave police access to Nunn's Twitter account. They're hoping info from the account will shed some light on where he is right now.