Will had gotten too close.

Too close to Hannibal. Too close to Jack. Too close to the FBI. Too close to these murders.

You and Will were partners, you were like Will, having empathy, and a knack for getting inside a killer’s head.

In bringing you on the field with him, he opened the doors to a visible vulnerability. You. Killers could spot weakness. Will had gotten too close to one, too close on their bad side.

Mason Verger. The man Will and Hannibal threw to the pigs. Mason was alive, somehow, and desperate for revenge. So he used you to get to the two.

Which is what brought Will back to the Verger mansion. Will wasn't one to kill, usually. But all he saw, the moment he saw Mason, was red.

He killed Mason, and his guards, and went searching the place for you.