Marvel has given us a couple exclusive teasers. It turns out that whoever has the Watcher's eyes, can discover all of the secrets of the Marvel Universe. When he was found, his eyes were missing.
It turns out that Thor is the one that discovers his body. Could these be suspects? That's how Marvel is billing it.
Here's a teaser with art by Agustin Alessio.
Here's another with art by Marco Checchetto.
Marvel released a couple more suspects on Marvel.com.
CBR posted a couple.
Newsarama also posted a couple.