But the other packages contained what appear to be live bombs. They were addressed to Hillary Clinton, Barack Obama, former CIA director John Brennan via the CNN office, former Attorney General Eric Holder, and representative Maxine Waters. Billionaire philanthropist George Soros also received a similar package on Monday. CNN described them as “rudimentary but functional” pipe bomb devices, containing explosive powder and projectiles like shards of glass.

Pipe bombs have long been the explosive of choice among terrorists and guerilla groups without access to military-grade weapons. They were used way back in the 1886 Chicago Haymarket Riots, by New York’s “Mad Bomber” in 1940s and 50s, and in the 1996 Atlantic Olympics bombing. Without getting into the specifics, the pipe in a pipe bomb is filled with explosive material, and lit through a fuse. The integrity of the bomb depends on how well the pipe holds the explosive. While pipe bombs are relatively easy to make, they’re not the most reliable. Many explode in construction, maiming or killing the maker, or don’t go off at all.

Luckily for all involved, none of the bombs have detonated, and they’ll be important clues as law enforcement’s investigation progresses. “Having a fully intact device is huge,” John Cohen, a former counter-terrorism coordinator at the US Department of Homeland Security and law enforcement official for 30 years, now a professor at the Rutgers School of Criminal Justice, told Quartz. “The first and most important thing is they’re going to be looking at the packaging and the materials used to construct the device.” The materials could provide clues to law enforcement about where they were purchased.

The packaging could also be telling, and has already helped the FBI connect the bubble-wrap manila envelopes sent to Obama, Clinton, Brennan, and Soros, which all listed Florida representative Debbie Wasserman-Schultz’s office as the return address. This was also the case on a package misaddressed to Holder, which ended up being delivered to Wasserman-Schultz’s office. There could also be fingerprints, hair samples, or DNA on the device or packaging, Cohen said. Given that officials believe the package Soros received on Monday was hand-delivered, it could very well provide additional clues, it could very well provide additional clues.

Law enforcement will also solicit tips from the public, Cohen added. “Perhaps the person who built the device said something to a coworker, or a family member, or said something on social media.”

📬 Sign up for the Daily Brief

Our free, fast, and fun briefing on the global economy, delivered every weekday morning.