I thought the same thing. The only problem is that in Columbia, they were well trained former government/military/security types. In Iraq, those are the Ba'athists, i.e. Saddam loyalists in the main. OTOH, training is underway and experience is being had by the freedom wanting Iraqis. The bad guys' time is running out...
These gunmen were not loyalists to Saddam.
My bet would be "off-duty" Iraqi Army (just as some members of Los Pepes were off-duty Colombian cops who worked with folks like AUC founder Carlos Castano).
It's a VERY efficient way to deal with problems like the insurgency and the Sunni Arabs. :)