CHRISTOPHER DORNER CARJACK VICTIM SUES For $1 Million Reward

The man who was carjacked by cop killer Christopher Dorner hours before he was cornered in a cabin ... is suing the city of L.A. for the $1 million reward it offered to the public, but then pulled back over a loophole ... TMZ has learned.

In his lawsuit, Richard Heltebrake says Dorner commandeered his purple Nissan truck after jumping out of a snowbank and pointing a gun at him on February 12. He goes on to describe how Dorner used his truck during a shootout with law enforcement ... ditched it for a Fish and Wildlife vehicle and eventually fled to the cabin where he died.

Heltebrake is suing ... claiming he's owed a ton of reward money that was offered by the city of L.A., Riverside County and the cities of Riverside and Irvine. Three of those rewards were for "information leading to the apprehension and capture" of Dorner. Another was for "identification and apprehension."

The language is important because Dorner was not apprehend or captured -- but instead police say he died of a self-inflicted gunshot wound inside the burning cabin. 

As TMZ first reported, L.A. officials were hesitant to pay up -- and in the suit, Heltebrake claims all the municipalities denied him any money. 

Heltebrake wants at least $1 million -- as well as an order prohibiting anyone else from getting the reward money.