I'm a bit out of the loop... Anyone got a TL;DR for why he decided to come back to Russia knowing full well he will be arrested?
but then again, maybe Alexey or his supporters didn't expect him to be arrested this fast
Strangely enough the Russian government still want to appear to have a legitimate democracy, probably caring more about the appearance to the governed rather than to outsiders.
He wanted as much attention as possible. He can't do anything from Germany and neither from hiding somewhere in Russia. So this was his best shot right now.