Adachi's Transfer

It's a question that's been bothering me for a while, but why was Adachi transfered?

We can assume, by going on Adachi's character, that it was probably rather serious, but Adachi didn't see it that way. He most likely thought that it was 'no big deal, something silly, that all those idiots overreacted over'.

But the thing is, what?

I've asked this question before in various places, and someone said that perhaps he might have killed someone, or 'shot a hooker'. I think this is highly unlikely, as if he did kill someone, he wouldn't just be transfered. He wouldn't even have his job anymore! So we assume that it was serious enough for him to get sent out into the middle of nowhere, but not serious enough for him to lose his job, or have something on his record.

And if Adachi wasn't new to the job, why does Dojima constantly treat him like an intern, sending him on endless coffee runs and the like? If he got transfered, surely it would have been in his file. And since Inaba is a fairly small town, if the police station was getting a transfer, Dojima would certainly know about it, and would've looked into his previous files. Unless Adachi still was a newbie, and did something silly during his first few weeks in the city.

Someone said that it might have been something to do with political reasons, that perhaps Adachi slandered someone powerful which caused a huge fuss, and he had to be sent away until 'things calmed down'.

I'm interested in hearing everyone's thoughts on it. :)