WASHINGTON — Investigators examining the explosive devices sent to high-profile targets in Washington and New York this week 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.

Larry Johnson, a former head of criminal investigations for the U.S. Secret Service who also served as a special agent in charge of the presidential protective detail, said that 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. “There will be no stone left unturned.”

Johnson said it is highly likely that the person or people who built the bombs had been previously flagged by law enforcement. The Secret Service maintains an extensive database of individuals and groups who have made past threats against presidents or other top political leaders, either through letters, emails or on social media.

Among the first steps for investigators will be retracing the path of the packages through the postal system or courier service used to deliver them.

The U.S. Postal Service operates a sophisticated imaging system that photographs the outside of each piece of mail processed across the country and can be used to determine the specific location of where it was sent. That’s how federal officials were led to a woman who sent the poison ricin through the mail to President Barack Obama and then-New York City Mayor Michael Bloomberg in 2013.

The envelopes and packaging materials themselves will also be closely scrutinized.

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. There may also be fingerprints or hair.

Because the devices were intercepted before they exploded, forensics experts will be able to carefully disassemble the devices and examine the components. They’ll examine the wiring, the initiating system, any timing device. If it was a pipe bomb, authorities will seek to identify what type of pipe. The design of the bomb will be compared to devices recovered in the past.