That is, I'm sure he understands that this action might be interfering with an investigation, and that it's reasonable to believe it was a willful act on his part.
Can you get into trouble for doing something like this?
No. This does not affect their ability to use it. This certificate is simply no longer trusted by other parties (rightfully, because it was compromised).
As matter of fact, this may not even be his doing.
What if the 3rd party the FBI wanted to intercept via this Cert has now been 1) notified that there is a problem and 2) can no longer be intercepted (unless their browser does no CRL or OCSP checks on the domain's cert)?
No, that's not the point I was trying to make. The people in Washington D.C. that sit in fancy leather chairs have repeatedly demonstrated their lack of critical thinking skills, so I use terribly bad sarcasm to illustrate what their puny brains will think of next.
Interesting point. AFAIK they requested the key to decrypt previous communications. From security point of view, his move makes perfect sense. If FBI wanted to decrypt future communications, they would probably have specified that in their request. Then he would indeed break court order and could be hold responsible.
On the other hand, it would be hard to prove any actual obstruction, since the service was shut down and all users notified about this whole situation.
The same day that everyone agreed "Roadside Safety Checks" (police looking for drunk drivers under the auspices of checking children's carseats at 1AM) was the lesser of two evils (Drunk drivers killing innocent people is a greater evil than everyone's 4th amendment rights being violated).
To a lesser extent, anytime that politicians frame an issue with the two phrases "it's for the good of the public" and "it's not a problem if you aren't guilty", they're generally trouncing a constitutional right, or greasing the tracks for it to inevitably happen.
When it comes to public safety, the American people stand ready for intrusions of all kinds, it is truly for our own good. Government agents are privy to secret information unknown to the public, therefore we have no choice but to submit.
That is, I'm sure he understands that this action might be interfering with an investigation, and that it's reasonable to believe it was a willful act on his part.
Can you get into trouble for doing something like this?