My sympathies go out to you. I doubt that this will be of any comfort, but I can think of two reasons that they may not be releasing information.
First, based on the events you describe they may think that they're protecting family by not allowing you to see the body. It's also possible that forensics may still be in progress.
Second, and more likely, the police are probably concerned that grieving family members may go vigilante, possibly taking vengeance on the wrong people, and they want to avoid being distracted from their investigations.
Quite understandably, you want a fast resolution to this, but the police deal in volumes of cases, and every one is a tragedy for each victim and their families. Most often police set up procedures to isolate themselves from pressure by families and having to make frequent reports to them. Unless you have connections within the force, they'll probably shut you out just as they have thus far.
I hope that your brother gets justice, but for your own well-being, you should try to approach this as a long, often frustrating process. Also, and I know this is hard because this I can hear the frustration in your post, but remain respectful and polite -- in general and like everyone else, cops tend to be less cooperative if they feel someone is "in their face"; because of the nature of the things they deal with, they may even react worse than most folks, and it won't help you get what want if you piss them off. You might try to find a local victims support group -- they'll probably have suggestions about what, if anything, you can do to get information most effectively.
