That's a *nice* piano. Is it a Steinway & Sons Model Z? The Regent has exquisite tastes!

That's probably the piano of the late Empress!
Corvo obviously wanted the Lord Regent to KNOW why he came to him. "You STOLE my piano, you poor sob! Now feel the wrath of a thousand strings hammered at the same time!"
We can clearly see blood spurting from the Lord Regent's ears (ok that his neck, let's pretend, kay?

)
On topic, I broadcasted the confession without him even noticing I was here.. I think if the bodies physics were as "non-realistic" in Dishonored than in Skyrim, I'd get a lot more of fun. In Skyrim, I always felt the urge to throw the bodies down the waterfalls, empale them on pointy bloody spikes, drag them to the most visible place, for all to see and fear the Dragonborn's name. Guess that's the barbarian setting.
Corvo's much more refined : he just drops bodies in dumpsters or leaves them on tiny little airducts with the hope they will have a pleaaaasant wake-up later on.