Mr. Pink is also an undercover copPink is the only one of the 4 guys actually focused on who never has his name revealed. He has no backstory, insists on acting professional at all times (as if he's somewhat new to the whole heist thing and doesn't treat it with the same aloofness as the others), and says that he's been shot after he runs outside the warehouse, despite not actually doing so. He grabs the diamonds before running out, where he... immediately surrenders. What would be the point of taking the bag with him if he just surrenders unless he's working with the cops to safely retrieve the case and just says he's been shot so he doesn't get shot by the rookies who aren't in on the plan. Also, his insistence on moving the whole ordeal to a new location could have been a ruse to lure the others directly into a trap and have one of the then-missing guys call Joe Cabot to the warehouse & have the cops move in.
- This is unlikely. His professional behaviour suggests experience or just a way of behaving that fits this situation. He most likely didn't know that the police were outside when he ran out with the diamonds. His lack of backstory just indicates that he's an outsider compared to Blonde or White. Finally, if he was an undercover cop, then he most likely wouldn't be so gung ho about shooting at other cops in his escape. There are definitely good hints towards this theory, but I think it can be discredited as well.