Lots of Artistic License
I've seen this movie twice--first time the last half or so, after he is in and "doing his thing," and last night the whole way through. It is a good psycho thriller, but Keaton's stay wouldn't have lasted that long. And I'll avoid the movie in the future...to slow and ridiculous.
I've been a tenant more times than a landlord and, yes, tenants have an enormous amount of rights, but wanton destruction of property isn't one of them. Every lease I have ever seen had a clause that indicated damaging or destroying property was cause for eviction and the tenant was responsible for the damage. Certain changes were OK--curtains, and painting (with owner permission), but to do what he was doing and continue to live there? Sorry, don't buy it. Locks cannot be changed. Despite the "tenant rights", landlords do have entry rights, normally in the case of emergencies, but can gain entry with a warrant.
The arrest scene after the fight? I can't write LOL enough to cover the absurdity of that scene. The cops drive up, handcuff Bodine, throw him in the back of the car and drive off without any investigation? Plus, any investigation would have discovered that the timing between the 911 call and the fight were backwards.
I'm not sure who was "dumber" in this show--the couple or law enforcement.
On the other hand. Thinking of being a landlord? Have an airtight lease and do background checks. This "might" save you.