As former leaders of the FBI task force that caught the Unabomber, Ted Kaczynski, in 1996, we know how urgent it was for law enforcement to track down the source of the bombs. It took the FBI 18 years to identify and capture the Unabomber, and that was too long to be repeated this time around.

Below are the most valuable lessons we learned in tracking down the Unabomber. In moving so quickly to identify probable cause supporting Sayoc’s arrest, we have reason to believe those same lessons were applied by the FBI over the last few days.

Look for signature bombmaking habits

Investigators execute a relentless forensic examination of all bomb materials and their packaging, including mailing labels, stamps, and mailing markers sometimes attached in transit by the U.S. Postal Service. Certain materials are been scanned for DNA evidence by the FBI Laboratory and bomb technicians to determine if there are similar characteristics among the materials or in the handicraft of the bombmaker. They ask other government agency crime laboratories to see if they have processed bombs of similar construction, since serial bombers develop a recognizable signature in their bombmaking skills and habits over time.

In the Unabomber investigation, we found inconsistent evidence processing standards among the multiple federal and state law enforcement laboratories that worked on separate facets of the case. That was remedied when the FBI Laboratory developed uniform standards that apply in a task force environment, such as the inter-agency collaboration process utilized in the mail bomb case.

Rely on mail inspectors

The U.S. Postal Inspection Service was able to work miracles in nailing down where the Unabomber had mailed some of his package bombs. Sometimes the service even identified the employee who processed the package in the mail stream. Its inspectors used video-based training for post office employees to demonstrate to them what suspect packages look like. This was a vital tool that was likely exploited again in the current bombing investigation.

Zero in on physical locations

The Unabomber both mailed his bombs and placed his devices near physical targets, which differs from the current serial bomber, who appears to have so far only struck through the mail. But the investigative tactics we used when Kaczynski placed his explosives could have been applied in the current case.

Regardless of how an explosive is delivered, the bomber must at some point physically visit an area to either mail a package or place a device. During that process, they always run the risk of catching the attention of an eyewitness. This is exactly what happened when the Unabomber left a device in a parking area behind a computer store in Salt Lake City. He was spotted, and the eyewitness gave his description to a police artist. The result was the iconic drawing of the Unabomber wearing dark sunglasses and a gray hoodie sweatshirt.

The usual strategy to find a bomber is to match the investigative response to the bomber’s predictive behavior. With Ted Kaczynski that meant taking a wider scope of inquiry because of his varied methods, whereas in the current case the bomber’s pattern involved consistency in construction and delivery methods.

When the Unabomber was active, we had no advanced computer systems or Internet. After a bombing, we relied on flooding the surrounding neighborhoods and businesses with investigators, who talked with people to identify potential eyewitnesses. Nowadays, we have the benefit of not only more and better security cameras, but cell phone cameras in nearly all of our pockets. With camera footage in and around mail delivery centers, investigators can be led to actual eyewitnesses and possible suspects. And the FBI can now deploy facial recognition software to enhance its ability to search out individuals from that footage.

Find patterns and focus resources

The Unabomber exhibited no regard for who was killed or maimed by placing some of his bombs in public places. In other instances, he directed bombs through the mail to specific people that he wanted to kill. For years, this unpredictable pattern made it difficult for FBI agents to know exactly how to deploy their resources in finding a suspect.

In the current situation, the bomber followed a more predictable and logical pattern. Having a consistent pattern allows investigators to focus their resources. The Unabomber started by targeting Chicago, so we surmised that he had probably gone to school or lived there. Analysts began collecting information on vehicle and property owners in Chicago and putting that into a huge database, where it was cross-checked against suspect lists. Then, we began working in his attacks on different locations at different dates, and tried to find some kind of trend.

Now, with artificial intelligence technology, the FBI should be more efficient in quickly analyzing geographic, chronological, and residential data to narrow down a potential list of suspects. This technique of cross-checking the data was invaluable to us in documenting the Unabomber’s physical presence in specific city locations when bombs were either placed or mailed. This provided the primary elements of probable cause authorizing our search of Kaczynski’s remote cabin in Montana.

Looking ahead

The arrest of a suspect marks the end of a manhunt and its accompanying media storm. But for those in the FBI and U.S. attorney’s offices assigned to this case, the focus of the work moves into the structured environment of the federal courts, where probable cause and admissible evidence are the priorities of the day.

During the investigation, coincidences will have been abundant and often meant nothing. Personal theories and political ideologies may have become distractions. But now, the rule of law will embrace only the facts.

Lessons from the Unabomber case helped the FBI catch the current suspect, and perhaps they will continue to be instructive for the future generation of law enforcement.

Jim Freeman is the former special agent in charge of the San Francisco division of the FBI that oversaw the multi-agency UNABOM Task Force. Terry D. Turchie is the former assistant special agent in charge of the UNABOM Task Force. Donald Max Noel is the former supervisory special agent of the UNABOM Task Force. They are the co-authors of Unabomber: How the FBI Broke Its Own Rules to Capture the Terrorist Ted Kaczynski. They are all currently retired.