This is the only one I'm aware of that is actually a common saying. It would help if we got a more context for the Italian. Who might be saying this? Children? Adults? Police officers?(At the risk of being both irrelevant and gross, I'll add that the first saying that came to mind was "he who smelt it, dealt it"--what kids say to each other when someone says "ew, what's that stink? Did you fart?")
I can see your point, in italian we have 2 terms to translate suspicious looking person (sospetto - ex. c'era un uomo sospetto che vagava per la strada) and person who suspects/doubts of the others (sospettoso - ex. il Commissario é sospettoso perchè la versione dell'indiziato non lo convince).Maybe it's just me but I was going to say that the only problem with "suspicious people" is that there are two meanings. One is people who don't trust others and the other is people who are themselves questionable, unsavoury. For example "There were some suspicious (looking) people hanging around in the alley."