Putting someone under 'house arrest' doesn't necessarily mean they believe he is guilty of anything. It is standard practice under such circumstances to avoid the possibility of any evidence being tampered with.

Would the Police leak sensitive information? Sounds odd to me.

As for the sewage tanks, I doubt that they would make that a high priority...!! Assuming they do have such tanks and don't already dump (!!) it straight into the sea...

I've heard it said they don't swim off the coast of Italy, they just go through the motions!