ARI SHAPIRO, HOST:
We begin this hour with more on the federal charges against Ahmad Khan Rahami. He's the man accused of planting bombs in New York and New Jersey over the weekend and injuring 31 people.
Federal prosecutors say Rahami bought some of the bomb components on eBay.
As NPR's Joel Rose reports, that underscores just how easy it is to make a powerful explosive from common materials.
JOEL ROSE, BYLINE: On Saturday night, NPR books editor Petra Mayer was staying with a friend on 27th St. in Manhattan. They were walking home when they noticed something on the sidewalk.
PETRA MAYER, BYLINE: I just happened to see this flash of silver out of the corner of my eye and looked down. And, literally, this was my thought process. Hey, there's a pressure cooker. But we looked a little closer and it was covered in duct tape. And I think that was the clue that something was not OK.
ROSE: Mayer and her friend went upstairs to the apartment and called 911. She says they learned the next morning that they'd found a bomb that didn't go off.
MAYER: The first thing you think is not bomb. The first thing you think is somebody just didn't want their pressure cooker. It was only a few degrees off of what would just be a piece of street junk.
ROSE: And it's not just the pressure cooker itself.
MICHAEL O'NEIL: Unfortunately, to make an improvised explosive device is really not that difficult.
ROSE: Michael O'Neil is a former commanding officer of the NYPD's counterterrorism division. He's now the head of MSA Security, a private firm in New York.
O'NEIL: You don't need special tools. You could source the materials right off the Internet.
ROSE: That's exactly what prosecutors say Ahmad Rahami did. According to court documents, Rahami ordered parts for his pressure cooker and pipe bombs from eBay, including ball bearings, circuit boards and a system for igniting fireworks.
The court documents don't go into much detail about the explosives used in the bombs. But O'Neil says it could have been a compound called HMDT, which can be made from legal and harmless products like citric acid and peroxide.
O'NEIL: For a peroxide-based explosive, you really need high concentration peroxide. It's not something you'd find in a typical drugstore. But you would find it in a beauty supply store. It's for, like, dyeing hair. So it's a - has a great use in everyday life for beauticians.
ROSE: But that makes it hard to prevent these materials from falling into the hands of a bad actor.
At a press conference today, U.S. Attorney Preet Bharara of New York says that's why there are so-called trip wires in place to notify authorities when someone places an unusual order.
(SOUNDBITE OF PRESS CONFERENCE)
PREET BHARARA: We have gotten a lot better at making sure there are trip wires when people are buying things that might be suspect. But there are limitations to that when people are buying things that are not inherently unlawful or explosive.
ROSE: Of course, it takes a certain amount of skill to turn ordinary household items into a bomb. Prosecutors have not said where they believe Rahami learned the trade or if he was self-taught. Authorities are investigating trips he took overseas to Afghanistan and Pakistan. But instructions on how to build an improvised explosive device, or IED, are widely available on the internet.
BOB MORRIS: If somebody wants to build an IED, they're always going to be able to build an IED. IEDs have been around in one form or another for centuries.
ROSE: Bob Morris is a retired Army colonel and founder of the Global Campaign against Improvised Explosive Devices. Morris says one way to fight IEDs is to educate the public and law enforcement about what to look for.
Prosecutors in New York say they've recovered a cellphone video of Rahami testing one of his explosive devices a few days ago. He seems to be in a backyard.
MORRIS: That should have been an indicator to somebody to call in and make a complaint about it.
ROSE: Morris says the sound would have been louder than fireworks. But if anyone called law enforcement to complain, the court documents don't mention it.
Joel Rose, NPR News, New York. Transcript provided by NPR, Copyright NPR.