I'm having a bit of hard time to actually picture the posture of someone that tries to open that window from the ledge. I'd expect the glass to be be removed further up to provide a better working space to actually open the latch. Stooping or kneeling down on the ledge might be possible, but with the glass that still was there it seems like an invitation to get your legs/knees cut up. Doing it while dangling from the ledge seems a rather precarious alternative, because your hand would likely end up on the glass when you try to lift up enough to reach the latch.
It's also curious to me that none of the fragments of on the ledge seem to have fragmented further from pressure put on them.
Sorry if I reiterate that part, it keeps bugging me.
I've also been looking if there is another bigger/less cropped version of
http://blog.seattlepi.com/dempsey/library/WindowLawyerScaling.jpg around. I seem to recall there is one but have been unable to locate it.