Who will watch the watchers? Some guy on a train with a Twitter account, it turns out.

The former CIA and NSA director Michael Hayden ended up on the wrong end of a surveillance stakeout on Thursday afternoon when, while riding a commuter train, he was overheard "disparaging" the Obama administration. The over-hearer was a private citizen – Tom Matzzie, an entrepreneur who previously worked for MoveOn.org and John Kerry's 2004 presidential campaign.

Hayden was aboard an Acela train outside Philadelphia and talking by phone with a reporter when Matzzie, who was sitting nearby, recognized him. Matzzie heard Hayden insist to the reporter that he be quoted anonymously, as a "former senior administration official".

Then Matzzie began live-tweeting as the nation's former top spy badmouthed the Obama administration, apparently in connection with the revelation hours earlier that NSA had monitored the phone calls of at least 35 world leaders' telephone lines.

Former NSA spy boss Michael Hayden on Acela behind me blabbing "on background as a former senior admin official" Sounds defensive. — Tom Matzzie (@tommatzzie) October 24, 2013

Hayden was bragging about rendition and black sites a minute ago. — Tom Matzzie (@tommatzzie) October 24, 2013

On Acela: former NSA spy boss Michael Hayden just ended last of handful of interviews bashing admin. — Tom Matzzie (@tommatzzie) October 24, 2013

On Acela listening to former NSA spy boss Michael Hayden give "off record" interviews. I feel like I'm in the NSA. Except I'm in public. — Tom Matzzie (@tommatzzie) October 24, 2013

On Acela: Hayden's comments to press were clearly about NSA spying on foreign allies. #haydenacela — Tom Matzzie (@tommatzzie) October 24, 2013

The episode came to a remarkable conclusion shortly after Matzzie noticed Hayden receiving a new phone call, and joked on Twitter that Hayden's office must have heard what was happening and called to warn the former spy chief.

On Acela: phone ringing. I think the jig is up. Maybe somebody is telling him I'm here. Do I hide? — Tom Matzzie (@tommatzzie) October 24, 2013

Matzzie’s hunch was right — but as it turned out, he didn’t need to hide.

Me and Steeler fan Michael Hayden. pic.twitter.com/vOmr6RIMPe — Tom Matzzie (@tommatzzie) October 24, 2013

On the pic. His office called him and then he graciously offered me an interview. We talked around the 4th amendment and foreign spying. — Tom Matzzie (@tommatzzie) October 24, 2013

I just had a very nice conversation with Michael Hayden. He was a gentleman and we disagree. — Tom Matzzie (@tommatzzie) October 24, 2013

At the end of the episode, though, Matzzie admitted he didn't feel entirely comfortable about what had happened.