Congrats Rumble!!! And It ended with a happy ending, aww! I was lost this entire time, so these answers were kind of random:
1) Who killed Chief McGovern? = Chief McGovern Sarah Jordan.
2) Why did Chief McGovern die? = Alex, knowing how unaware his wife was, decided to have her go ask the chief for dating advice. When he refused, she pushed him into the fountain, unknowing he was H2Ointolerant.
Uhmm, no.
Sarah needed to take her stress out on something, and the Chief was the closest thing she could use.
Not that either. Okay, here's my real answer:
The chief, on his drunken spree, was going to arrest some crook. Sarah and Robbie got paranoid, thinking they'd be arrested, and killed the chief unintentionally. The rest of what happened was paranoia trying to catch the killers, while there really weren't any, just a big misunderstanding
3) Who was the accomplice? = Robbie Swanson