I get being fan sometimes means antagonizing the opposing fan base. When I was going to school in New York I loved to make fun of the Jets and Giants fans (this was back before Jerry Jones messed up the Cowboys). Even now I love to roast the Jets and their never-ending drama.
However, I firmly believe there is a line that you don't cross--and the Pittsburgh retailer that created this t-shirt certainly did.
I get making fun of the whole cheating scandal. That directly involved the franchise and the integrity of the game, but the 'murderers' comment is pretty poor. From a team perspective it is a gross incorerect characterization to equate the whole group to Aaron Hernandez.
But more importantly you are poking fun at an incident that cost a man his life. Have a little respect for the dead here Steel Town.