Also talk to the local councilmen and police because they're pretty aware of future projects. 

Police report will take an hour tops.

My thoughts first are:Discuss the issue with the neighbors stealing the waterTalk to the property owner--who is the epitome of a slumlordDocument their actions with a small video as I'm at the property often and take this evidence to the police and/or city.Thanks in advance.

There is a strong police presence there to keep the crime at bay.The roof is about 7 years old, relatively new ac units in 3 of the units, 2 long term tenants, the other two within the past year.

He only went off the police report that I filed before a contractor got involved with the clean up and discovering the extent of the damage.  

If I lock them out, will.the police make me let them back in or can they legally break in or is their only recourse civil court? 

@Patrick Hopkins 'The first duplex I actually made it a condition of the contract to vacate the current tenants prior to closing due to the condition and (backstory I am a police officer for the city my first building is located in) I had arrested the lower level tenants a few times.

I've got a full time job (police officer) and have no plans on leaving anytime soon (29 yo) but I want to get into the buy and hold rental market in the greater seattle area.

The crime is high in that area ... even though the 12th Street police station was recently built. 

Not much you can do except report it to the police and also pursue eviction and damages in court