Well, it was more a bad judgment call to do work for a gang that was stepping on Capone's toes. Last bit I saw, the mechanic had a couple of arrests for safecracking but was trying to go straight, but occasionally did repair work for Bugs Moran's gang.
Besides, the whole operation...it was a turf war, but the fake cops, the suits, the reassurance of bystanders by having the fake cops lead the plainclothed ones out. That's a lot different than the savage, animalistic, "b_tch! You disrespectin' my hat!" *BLAM* crap that goes on there today. Now, it's just people who place absolutely no value on life whatsoever....theirs, or anyone else's.