Of course gentrification pretty much always means rents and housing costs will go higher but it also pretty much always results in lower crime rates especially violent crime.

Could they turn violent?

I don't care how long its been or how "non-violent" they say they are.

Transported with passion or fury; raging; violent; as, a furious animal. 2.

If you are victim of a violent crime, the motive is usually robbery or rape (or both) which sometimes escalates to murder.  

Hawaii has a very low violent crime rate per capita, with honolulu having half the population of Indy but significantly less crime.

Wow, amazing story, there was no mention of names and a violent reaction was triggered.

Areas like Brooklyn have seen a dramatic increase in violent crime (homicides especially). 

I personally don't care about purchasing a property where a violent crime occurred, but the issue is disclosure.

It was a non-violent scam(see below for how I figured this out) -  tenants would respond, then the scammer directed them to a fake credit processing site where the mark would pay $40 or so to get a credit report.