Another thing I wanted to add, as I feel it is important: I do believe Hendry's analysis, that Guded was surprised by MK's early return, and responded by killing her. Considering that prior to this, he had only been a petty thief, makes me deduce that taking this huge leap to killer was due to the fact that he really did enter via the broken window.
Because: If he had been let in by AK, he could have gotten out of the bind, by saying to Meredith, "Hey, sorry, I was using your bathroom, Amanda said no one was home tonight and I could hang out here, but I will be going now, really sorry". The worst MK could have done was be mad, maybe say something like , "Well, why did she say you could hang here? I really do not appreciate this!" But to feel he had to kill her, to use the knife, I believe Rudy must have known MK could see that she was coming in on a robbery in progress, as Hendry asserts - and that he had entered unlawfully, and consequently was destroying his relationship with the guys downstairs, and would now be known as a criminal, & would be arrested and shamed in Perugia - Hence, he felt he had no choice but to kill her. He had been lucky til then; now his luck had run out.