With jstat you will only see the memory in total.
If you gan figure out that the bottom line of memory is growing up and never come done this is an indication for a application memory leak.
You might try what Radoslav mentioned and dump the heap two times, e.g. after a while when JBoss was started and before crashing.
A comparsion between such dumps with jProfiler will show the what number of Objects are increasing.
But be aware that you must use more memory to analyze it.
Other option is to do it with jProfiler in a test environment, start the UseCase take a snapshot, start it again (fire a GC with jProfiler) and compare it with the snapshot.
It might be easier and do not harm the production environment.