We have the documents for their reasoning. The stated reason was because the mob used handguns for assassinations, they didn't give a rats ass about some bank robbers in the middle of nowhere at the time, but the mobsters were fucking with them on the east coast so they just had to get rid of handguns. Then someone brought up the fact that cut down barrels on rifles and shotguns would be a loophole so they added it in. Then, they decided that the handgun ban wouldn't pass SCOTUS so they dropped it, but left the barrel length in.

They don't mention any one event or person in the documented debates, just organized crime in general.

They have zero documented discussion on suppressors.