Among the findings:

■ ATF agents befriended mentally disabled people to drum up business and later arrested them in at least four cities in addition to Milwaukee. In Wichita, Kan., ATF agents referred to a man with a low IQ as “slow-headed” before deciding to secretly use him as a key cog in their sting. And agents in Albuquerque, N.M., gave a brain-damaged drug addict with little knowledge of weapons a “tutorial” on machine guns, hoping he could find them one.

■ Agents in several cities opened undercover gun- and drug-buying operations in safe zones near churches and schools, allowed juveniles to come in and play video games and teens to smoke marijuana, and provided alcohol to underage youths. In Portland, attorneys for three teens who were charged said a female agent dressed provocatively, flirted with the boys and encouraged them to bring drugs and weapons to the store to sell.

■ As they did in Milwaukee, agents in other cities offered sky-high prices for guns, leading suspects to buy firearms at stores and turn around and sell them to undercover agents for a quick profit. In other stings, agents ran fake pawnshops and readily bought stolen items, such as electronics and bikes — no questions asked — spurring burglaries and theft. In Atlanta, agents bought guns that had been stolen just hours earlier, several ripped off from police cars.