It was really offensive, and he made the jokes right after people had been killed which was even more offensive, and he didn't even put it on his own blog but injected that crap into the product.
Complimenting someone's writing doesn't mean you endorse their actions, and the killer's sister being attractive is relevant when the killer was motivated by sexual frustration. Sometimes we need to talk about things, even though people might be offended, or, in Gawker's case, act offended for attention and/or page views, another way of exploiting tragedy.
Another example: http://history.genius.com/Kurt-cobain-kurt-cobains-suicide-n...