The United States was forever changed by the events that took place in NYC on Friday, February 26th, 1993.  It was the first terrorist attack by Middle Eastern extremists on U.S. soil.  On the second floor of the parking garage underneath the World Trade Center tower 1, an explosion occurred that left a crater 150-feet wide by several stories deep AND high.  A forensic investigation was launched that involved chemical and physical analysis of the samples, analysis of the explosives scene, and forensic accounting.

Chemical Analysis

The FBI was one of the investigative agencies involved.  At the time of the explosion, Dr. Bruce McCord, my former graduate school adviser was an explosives researcher for the FBI in Quantico.  Some of the novel methods of explosives analysis developed by McCord and coworkers were used to help determine the chemicals found at the scene.  It was eventually determined that the explosive was over 1,000 lbs of urea nitrate.

The forensic investigators had a difficult time determining what explosive was used in the bombing.  As I mentioned above, it was determined to be a urea nitrate bomb, however, urea and nitrate individually were found all over the place in the parking garage after the explosion.  Urea’s presence was largely due to road salt and sewage.  It was wintertime and NYC used bio-friendly urea as ice melt.  There was also eighty pounds of sewage covering the area due to busted sewer mains.  Both of these factors contributed to the urea.  Nitrates were present in the parking garage due to the prevalence of acid rain as well as from automobile exhaust.  Individually, the presence of urea and nitrate was legitimate.  This made it next to impossible to determine that the explosive was urea nitrate.  As a result, the chemicals from the scene were inconclusive, but drums containing the chemicals used to make urea nitrate were discovered as you will soon read so it’s hard to believe it was anything but urea nitrate.

• An aside: As a result of this issue, one of my major dissertation projects was an environmental survey performed in conjunction with the FBI to determine what types of ions are ubiquitous in the environment.  It is important for forensic investigators to know this in order to determine what is potentially present from a crime scene and what was already present in the surrounding environs.  I will discuss this more in my next post.

Crime Scene Analysis

The big break in the WTC bombing was from a vehicular fragment.  Forensic scientists were unable to collect explosives residue due to the sewage contamination, but a VIN—vehicle identification number was located and traced to a Ryder truck rental in Jersey City, NJ.  Now here is a piece of history that every law enforcement agency would wish for during an investigation.  Mohammed Salameh, who rented the truck, reported that it was stolen the day before the explosion and called wanting to get his $400 security deposit back.  Needless to say, authorities were ready and waiting for him when he went back to collect.

Forensic Accounting

Thanks to a search of Salameh’s possessions, investigators discovered Nidal Ayyad, a chemist working in NJ.  They were able to find traces of urea nitrate and other explosives at a safe house.  Further investigation led to a storage area rented by Salameh that housed urea as well as other chemicals commonly used for making explosives.  A letter was received in early March by the New York Times claiming responsibility for the bombing.  DNA from saliva on the envelope was matched to Ayyad.

Forensic Science is a Team Effort

This investigation is a good example showing that oftentimes it takes multiple forensic disciplines to solve a crime—especially a big case like this.  Cooperation not just across disciplines within an agency, but across agencies is a must in order to answer the important questions: Who did it?  How was it accomplished?, etc…