Wikipedia article of the documentary.

Dowd describes being under-appreciated for the amount of work he put in and hurting for money as the reasons for taking money from drug dealers. He initially began taking bribes from drug dealers on the streets before moving on to protecting a drug cartel leader and robbing other drug dealers at gunpoint. Dowd and his then-partner Henry “Chicky” Guevara recount the first time walking into a domestic dispute in an apartment and seeing bags of marijuana, a duffle bag filled with approximately $20,000 in cash and two guns. Dowd communicated that he and his partner would take $8000 from the duffle bag and both guns. Dowd continued to rob drug dealers for thousands of dollars.