As authorities investigate a series of pipe bombs sent to high-profile Democrats and CNN, they will methodically search through various clues — including ones the sender may not have even realized were left behind — to home in on who is responsible.
Criminology experts say it is too early in the investigation to build a solid profile of who might be behind the suspicious packages, which were sent to former President Barack Obama, Hillary Clinton and others, as well as to CNN's newsroom in New York.
Unlike other fear tactics or more personal acts of violence, such as stabbings or gunfire, mailing threatening packages keeps the offender — or offenders — at a distance from their victims. But that does not necessarily mean they are guaranteed anonymity, said Tod Burke, a retired criminal justice professor and former Maryland police officer.
"This is a method they feel they can do anonymously, even though they’re really not anonymous. They are leaving evidence, they’re leaving telltale signs," he said. "There's always a signature somewhere. Bombs and things like that, there are signatures, as much as they may try to avoid it. In fact, sometimes by trying to avoid it, they're leaving more signatures."
Forensics will play a major role in identifying suspects, Burke noted. Authorities will check for fingerprints, DNA and any hair or fiber that may be preserved inside the packages.
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If the packages have any handwriting on or in them, that could also offer hints into the personality or even nationality of the sender based on how letters and numbers are formed, said former FBI profiler and NBC News criminal analyst Clint Van Zandt.
Mail-bomb suspects tend to be white males, he said, while cautioning that it is premature to make any determinations about suspects in this case.
And just because the intended recipients of the packages all seem to be political targets of conservatives, that does not give any definitive indication that the sender or senders share that viewpoint.
"You have to be careful. While it may well be the case that this is some radical conservative Republican, investigators are going to do a two-track investigation," Van Zandt said. "They'll say yes, that is who it is. Or, what if it's someone trying to push us that way, but it's the exact opposite?"
Henry Willis, associate director of the nonprofit think tank RAND Corporation's homeland security research division, reiterated that it was too early to guess what the specific motive may be.
"One thing history tells us is not to jump to conclusions about motivations. It also shows us that there could be many potential motivations," he said, citing terrorism to political discord to some combination of factors, including mental illness.
No one has been hurt by any of the devices, which authorities said appeared to contain live explosives.
The way the pipe bombs were constructed does not necessarily mean the sender has training or experience in bomb-making, Van Zandt said, citing the Austin, Texas, bomber who killed two people and then himself in March after apparently learning how to make explosive devices from the Internet. Experts say authorities will examine the devices to see if they bear hallmarks of any particular terrorist group's bomb-making instructions.
They will also look for basic clues: Have the targets received any threatening messages? Do surveillance cameras show someone delivering the packages, or dropping them off somewhere? Did anyone witness any strange behavior recently, such as unusual purchases at a hardware store that could be used to make such devices?
Eric Witzig, a retired homicide detective with the D.C. Metro Police, former FBI crime analyst and the vice chairman of the Murder Accountability Project, said there was a high probability that whoever sent the packages is following the news coverage and feeding off of the resulting sense of fear in the public.
And while there are still many unanswered questions — including whether all packages were even sent by the same person or group — Witzig said he had confidence in law enforcement.
"He or she will be identified. There is no doubt about that," he said. "It's simply a question of time and thorough investigation, and then this person will be arrested."