Investigators examining the explosive devices sent to high-profile targets in Washington, D.C., and New York will be working to glean forensic clues to help identify who sent them, gathering fingerprints and DNA evidence while tracking the origin of the packages and the components used to make the bombs, the Associated Press reports. Larry Johnson, former head of criminal investigations for the U.S. Secret Service, said bomb makers usually leave evidence behind. “If there is a human involved, there is a high probability you’re going to get somewhere investigatively,” he said. Johnson said it is highly likely that the person or people who built the bombs have been previously flagged by law enforcement. The Secret Service maintains an extensive database of individuals and groups who have made past threats against top political leaders, either through letters, emails or on social media. “Those looking to do revenge or harm to someone, it doesn’t just come to them one day,” Johnson said.
The U.S. Postal Service operates a sophisticated imaging system that photographs the outside of each piece of mail processed and can be used to determine the specific location of where it was sent. That’s how officials were led to a woman who mailed the poison ricin to President Obama and then-New York City Mayor Michael Bloomberg in 2013. “It will be a treasure trove of forensic evidence,” said Anthony Roman, a private security consultant. “As human beings, we are filtering off our DNA everywhere we walk, everywhere we sit.” Even the most careful bomber is likely to leave behind genetic material that could be used to identify them, especially traces of sweat, saliva or skin cells. Because the devices were intercepted before they exploded, forensics experts will be able to carefully disassemble the devices and examine the components.