This complaint sounds so harrowing that I looked it up. Here's what I found:
"On October 23, 2018, a 74-year-old male passenger was arrested and charged with physical assault of another passenger. The victim (a 73-year-old male) sustained head injuries and was medevaced to Hilo (Hawaii Island) via military helicopter.
Reportedly, he was using a public restroom on deck 7. When he opened stall's door to exit, an agitated man (from Nevada USA) confronted him. They exchanged words. While attempting to leave the restroom, the victim was kicked in the leg, fell down and hit his head on a toilet.
The incident occurred during the 16-day Hawaiian Islands cruise (itinerary Oct 20 - Nov 4) roundtrip from homeport Los Angeles (California) to Hawaii (Hilo, Honolulu, Nawiliwili, Lahaina) and Mexico (Ensenada)."
So - a couple of questions.
Did Princess Cruises make an announcement about what happened? If not, given your understandable concern, did you speak to the crew and/or captain about what happened? Or did you just believe wild rumors? (It appears that no-one was "brutally beaten to death" and it's unclear to me where that "information" came from.)
What happened to the attacker? Was he removed from the ship, or left to roam? Given that he was apparently arrested, it seems unlikely to me that the passengers would have been in any further danger.
Did you complain about the door locks? A ship that size (1,298 staterooms, according to CruiseMapper) most certainly has a maintenance crew that could adjust or replace locks, make repairs, etc.
Here's my view: Princess Cruiselines can't control the behavior of its passengers. Princess could not (presumably) have anticipated the behavior of this man. It CAN control how it responds to the situation. In this case, Princess should have made an announcement about an incident that could well have alarmed passengers (helicopter landing, etc.) and maybe given passengers some kind of freebie - a drink or something.
If Princess did NOT make any kind of announcement, and did not respond to your requests for reassurance, that might deserve some kind of compensation - a voucher for a future cruise or similar.
However, it does not seem realistic to me that any parent would spend the duration of a cruise frightened out of their minds about being murdered, or about their children escaping from staterooms to potentially fall overboard or fall prey to a roaming murderer, without doing something about it.
I'd need more details from both parties to make any kind of real judgment. However, on the face of it, asking for $54,000 some six months after an incident that was not in fact as described, seems unreasonable.