But they'll try their hardest to pin this on a scapegoat and he is the obvious choice. I'm not sure I'd cooperate either, particularly as lying to the federal government (any agency) is a crime within itself (18 U.S.C. § 1001) and even omissions or a poor memory can be argued that way (even if they're ultimately found not guilty the public would have lost interest by then).
I'd get a lawyer, say very little, and maybe give a written statement of facts to the investigators, nothing more.
The obvious choice, if there was to be a scapegoat (which I won't prejudge the officials involved to be seeking), until now was whoever designed/build the system in question (particularly it's UI), who had pretty much already been convicted in absentia in the court of public opinion (possibly based on fabrication, as it turns out.)
Now he’s the obvious choice, but that's almost entirely a result of his own actions.
His own actions being following sound legal advice..?
That excuse seems to work for our elected officials...
Choosing the wrong menu item should be expected and there should be safeguards to prevent an errant alert. If I click the "Close" instead of "Save" menu item in my editor, it asks me to confirm that I really want to close without saving. A civil warning system should have at least the same safeguards.
From public accounts, it doesn't sound like he messed up badly, he just made a minor mistake than anyone could make.