I think murders, assaults, rapes, and other violence happens almost daily here. Look at the number of sex offenders just in your own neighborhood:
https://sexoffenders.ehawaii.gov/sexoffender/welcome.htmlMost of the murders and assaults happen between family, friends and people who know each other. The random violence seems to be focused in the Waikiki area and involves tourists or bars after midnight.
I still have people tell me they never go to the North Shore after 9:00pm. The stories of people being beat up and robbed there are never ending.
A homeless man killed a tourist by pushing him into the Ala Wai Canal a few years back. Mental illness was blamed, but he'd been arrested some 70 times before.
Is Oahu dangerous? I think it can be, but not any more than any other similarly dense population center, maybe even less depending on time of day and location.
What I don't see here that i see in other places is a constant law enforcement presence. In NC, I could not drive more than a couple of miles without seeing a town Cop, a Sheriff or a Highway Patrol car. It's not that crime was that common, but that a police presence made anyone thinking of doing something wrong have second thoughts. Hard to get away after a crime if the cops are everywhere you go.