Law enforcement officials who are searching for a bomber can use his bomb as a road map, whether it has exploded or not. And rapid processing of the forensic material the bombs contain can often accelerate a manhunt.
Bomb experts tell NBC News that technicians can sometimes begin to zero in on a suspect by looking for certain clues that may include:
- What the components are and when and where they were purchased. Brand name, lot number, store location and date sold, all can help narrow down geography and provide valuable video footage and credit card information, among other evidence.
- Fingerprint or DNA evidence on the device. Authorities told NBC's Pete Williams that a fingerprint found on one of the explosive devices left in New York and New Jersey pointed them to suspect Ahmad Rahami, now in custody.
- Whether the explosive device matches others that have previously been detonated or discovered.
- Whether the style of construction of the device and the components used point to a particular avenue of radicalization. For example, al Qaeda's Yemeni affiliate has published bomb-making instructions online that list specific components.
- The sophistication of the maker. The quality and power of the device can reveal whether the bombmaker is well-trained, a veteran or a novice.
In the case of the bombings in Seaside Park, New Jersey and Manhattan, and the devices found in Elizabeth, New Jersey and Manhattan, the key to breaking the case was the fingerprint found on an unexploded device found in Manhattan. But police will also be looking at any similarities in design and components.
"Prior to an attack, authorities have slender threads such as radicalization and personal indicators," said one bomb expert. "By the time the perpetrator is located it is often too late. But moving fast to catch a suspect can prevent follow on attacks even if there has been some tragic damage before that occurs."