ARI SHAPIRO, HOST:
This next story is not an April fools' joke. The CIA recently used a school bus for a training exercise near Washington, D.C., and when the agency gave the bus back, they accidentally left something behind, explosives by the engine of the bus. Nobody was hurt, and we have invited NPR's national security correspondent editor Phil Ewing to explain how on earth something like this could have happened. Phil, how does something like this happen?
PHIL EWING, BYLINE: Well, the CIA does these exercises with local agencies outside of Washington school districts, sheriff's offices, police departments, etc. And in this case, they were in Loudoun County outside of Washington, and the scenario was for bomb-sniffing dogs and these other teams to respond to a bomb threat, I guess, at this school.
And we don't know whether or not the dogs found this bomb and they just didn't take it out from under the hood of this bus or whether they didn't find it and that's why it was still there. But at the end of the day when they gave this bus back, they had left these explosives under the hood in the engine block.
SHAPIRO: And so a couple days later, a school mechanic finds the explosives under the hood. And in the meantime - what? - a bus driver is just driving around a school bus full of children with explosives under the hood?
EWING: Yeah, that's exactly right. Now, we understand that there was no danger here. A bomb was not going to go off. These explosives used in these scenarios - they're very chemically stable. And in fact with some plastic explosives, you can set them on fire, and they still won't go off. They need an electrical detonator or pressure to make them go boom. But in this case, clearly it's not something you expect to find when you look under the hood of a bus, and the CIA had to acknowledge that, in fact, it was left behind as part of this exercise.
SHAPIRO: I can imagine the parents in this school district getting the email saying there were explosives under the hood of your children's bus. We're not thrilled about that. Why would the CIA even use a real school bus for this type of exercise? They have their own vehicles.
EWING: Well, the goal is to make them as realistic as possible. And we understand from the Loudoun County Sheriff's Office that this also involved a high school. So there were explosives for training inside the school as well, whether they were in lockers or a classroom or the gym as well as the buses. And the idea was to make this as realistic as possible for these CIA and local K-9 teams to come in, respond to the threat and find the explosives.
SHAPIRO: Well, as we said, nobody was hurt, and the CIA says nobody was even in danger. But a mistake like this has got to prompt some kinds of changes to policy, right?
EWING: Yeah, exactly. And, in fact, we understand those changes are in effect. They've suspended this program where they loan out these explosives to local law enforcement to do these trainings. And they've done an accounting of all the material they used, and they say they have it all. So right now, we do not believe there are going to be any more of these surprises where a mechanic or a custodian might open up something and find explosives inside.
SHAPIRO: NPR national security editor, Phil Ewing. Thanks, Phil.
EWING: Thank you. Transcript provided by NPR, Copyright NPR.