Here's a source that has done a lot of reserach on the question in anticipation of the Democrat attack.
Update - Ed Morrissey offers a synopsis. Read on:
This, at least, qualifies as a legitimate concern, at least legitimate enough that the state legislature has decided to investigate it. Supposedly Palin fired the commissioner of public safety because he wouldn’t fire her brother-in-law, a state trooper who had becomed estranged from Palin’s sister. Mike Wooten only got a suspension, and last month, she allegedly dismissed Walt Monegan over his handling of the case. Palin says that wasn’t the reason, the legislature noted that Monegan’s was a political appointment and he served at the pleasure of the governor, and they have also stated on the record that Palin has been so cooperative that they will not need to issue subpoenas — which hardly sounds like a cover-up.
So what did Wooten do, anyway?
Troopers eventually investigated 13 issues and found four in which Wooten violated policy or broke the law or both:
• Wooten used a Taser on his stepson.
• He illegally shot a moose.
• He drank beer in his patrol car on one occasion.
• He told others his father-in-law would “eat a f’ing lead bullet” if he helped his daughter get an attorney for the divorce.
Excuse me, but any of these four should have been a firing offense, let alone having done all four. He Tased his stepson? He threatened to shoot Palin’s father? No wonder the Palins hired their own investigator and pressed the issue so hard. But if this was the reason Palin cashiered Monegan, why did she bother to wait eighteen months after taking office to get rid of him?