Here's a notable instance of fake police, or rather, real police robbing banks in Iraq, from Joel Wing's blog.
First was the jewelry heist in Bayaa , a southwestern neighborhood in Baghdad. Before noon five SUVs drove up to a street filled with jewelry stores and set off bombs killing four, and wounding three. The gunmen then got out of their cars and opened fire on twelve stores, their owners, and guards, leading to eleven more deaths. They were armed with RPGs, AK-47s, machine guns, and silencers. To cover their escape the robbers threw grenades. On their way out they got into a gunfight with the security forces, wounding four policemen, before they got away. The Baghdad Operations Command claimed that they had killed one of the robbers, and arrested two others. The New York Times however, talked to a local witness who said that the dead man was not one of the robbers. Iraqi commanders quickly blamed the robbery on Al Qaeda in Iraq, saying that it was meant to replenish their coffers after their two leaders were killed, and many others arrested. The intelligence chief of the Interior Ministry however said that they didn’t know who the culprits were. The neighborhood was surrounded by blast walls and only had two entrances in and out that were blocked by checkpoints. Later, several senior police officers were arrested. It’s not clear whether they were directly involved in the attack, or whether they were just detained for negligence for letting it happen.
Three days later in the town of Mishkahb, 20 miles south of the city of Najaf, a branch of the state-run Rafidain Bank was robbed. A police officer served drugged tea to the guards at the bank. Then five other men entered, and made off with $5.5 million. A day later, $1.3 million of the stolen money was found, buried near a house of one of the thieves. The bank was holding such as large sum because it was going to pay government officials at the end of the month. The branch was just yards away from a police station as well.
Drugged tea? Joel also has reports on infiltration of the police in dear old Diyala.
If there is any conclusion to be drawn here, it's that this probably isn't good news.