Obtaining a "studio" is standard practice after a murder/fire or any unfortunate incident that caused someones death. The public, and the editors want to see the victim. Credit is given whenever possible but it basically falls under the same rules as any other image used for news. You don't need a signed release, you don't need consent. The photographer should be given credit for the image, everyone is regardless if it's a professional or family member that took the photo, they are credited. As for payment, it's rarely brought up because the family provides it. But if he wants a check he should get the standard rate, not some obscene number.
It's situations like this that give the media a bad reputation, a girl died and he's trying to make money off of it. Because the photo he took is the one plastered all over the news because she died, and there's no other reason it got this much play. If that girl didn't die no one would know his name and he'd be no better off financially than he was before the tragedy.
Also, do you have any idea how hard it is to get a photograph of someone who's been killed? It's one of those things they don't mention in journalism school or talk about in forums when everyone is going on about the "photojournalistic style" and all that crap. It really makes you feel like an asshole to ask a crying mother, brother, cousin, friend for a picture of someone they loved who was just shot in the head. But as the photographer who's responsible for obtaining images for a story, it's your job to ask and often it's more than once because the family has other things on their mind. And when the family had the time and willingness to bring out a photo, they didn't grab one from the family album, they grabbed a frame shot that was sitting on a table they got from this guy's studio. Because that's what was there. It was chance that his photo was the one that let the nation know who this little girl was.