APPARENTLY I JUST REALIZED THAT THIS IS FROM GILLIAN FLINN.
i've read this years ago and i found this so god damn good (I've read it in German) and today i held it in my hands as an English copy and i was ao confused why this sounded so familiar.
I really loved it and if you like psychotic stories you definitely love this too. Pluse i didn't know who the murder was until the last few pages.