Here's what the Secret Service is saying about the incident in 2007 involving Iranian president Mahmoud Ahmadinejad and an accidental firearms discharge:

In September of 2007, one of our personnel assigned to the Iranian presidential protective detail accidentally discharged one round from a Heckler & Koch MP-5 into the floorboard of a Secret Service vehicle while conducting an equipment inspection. At the time of the discharge the vehicle was parked in a motorcade staging area at the United Nations. There were no protectees or foreign security personnel in the vicinity of the vehicle at the time of the discharge. There were no injuries sustained by anyone as a result of the incident.

The Secret Service takes weapons handling and safety very seriously and a full investigation was conducted by our Inspection Division at that time. This matter was handled internally and in an appropriate manner.

In our book, we report that the incident happened in 2006; we got that wrong. 

As the incident was run up the food chain, here's how it played inside the Bush administration:

...President George W. Bush's daily intelligence brief contained a particularly chilling item. It was three sentences long, and it scared the hell out of the dozen or so White House officials cleared to read it. According to one official, it began, "A U.S. Secret Service agent, in an apparent accident, discharged his shotgun as Iranian President Mahmoud Ahmadinejad was loading his motorcade at the InterContinental Hotel yesterday."

At the time, the Bush administration was weighing how to deal with the Iranian nuclear-weapons program. And here a Secret Service agent had just given Iran a potentially devastating public-relations coup. Ahmadinejad was certain to reveal the accident in some grand form before the whole of the United Nations. He might allege that the United States had tried to assassinate him, and thus upend the entire conference. "When I read that, I remember closing my eyes," recalls the official.

The fact that Ahmadinehjad didn't say anything suggested to the administration that he might be more willing to deal with them privately than they had originally thought. A small incident on the margins of history, to be sure, but it's these types of things that tend to reveal as much as they conceal.