It's Hawkeye.

He knew the place would be double-bugged, so, he acted the part during the final moments of last issue.

Now, there's no body, and he's assumed dead, free to do whatever he needs to do.

Why did he off his family? Who is he working for, and why? I don't know. But, I'm going with Hawkeye.

Or Jarvis, because, othewise, he's a completely and utterly useless character designed to make lame 'poof' jokes.

But, it's Hawkeye...