Don't know exact charge against Proctor himself or if before all this or during. I mean the exact reason.
Currently there are no charges against Proctor.
The FBI doesn't generally go around inserting themselves in state crimes. For them to even get to the grand jury stage here is pretty remarkable and they must have had reason to do so. There are some anti-Karen Read pundits who insist the FBI only got involved because someone's wife had an axe to grind with the DA's office or because Yannetti was friends with someone. I can't buy such lame reasons. "Looking into" things is one thing. Putting together a grand jury is another.
The FBI did share information from their investigation into....something.... and this includes the information from Proctor's phone which is how we know he illegally searched Karen's phone (she voluntarily handed it over but he didn't have a warrant yet to search it) looking for nude pics of her and telling pals he wished she'd just kill herself. (Why is that, Mike?)
He's not going to get away with that, even if there is no way to definitively prove he planted evidence here. And yet he's still on the force. As a Massachusetts resident, I find this scary as there are other murderers out there who are in prison because of his work and it stands to reason some of them will get new trials once he's removed from office.
This puts the state in a difficult position. For instance, he's been the lead investigator on the Brian Walshe case, a guy who is alleged to have murdered his wife. He's awaiting trial. It's a tough case because there is no body. But I'm sure his defense counsel is watching the Read case closely, hoping Proctor is shown to be a fraud. Or is at least charged with violating Read's constitutional right against illegal search and seizure.
And this is why I think the DA has decided to push the Read case through, weak as it is. Jury is tricked by high cost attorneys into actually believing she's innocent! Crazy. Let's move on now.
The big question, which I think you've alluded to, is was the FBI already working on something related to state troopers, including Proctor, even before getting involved in the Read case. No one knows the answer to this. But I wouldn't be shocked to find out this isn't the first time he's done illegal things. I think he's behaved exceptionally boldly here and you don't just become exceptionally bold overnight.