The U.S. Postal Inspection Service


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Forensic Analyst Shirley Marc compares marks on a mail bomb component.

The U.S. Postal Inspection Service maintains a state-of-the-art National Forensic Laboratory in Dulles, Virginia, that houses highly-trained forensic scientists and technical specialists. These experts play a key role in the identification, prosecution, and conviction of individuals responsible for postal-related criminal offenses. Several units are part of the National Forensics Laboratory.

All the units provide support to the field through participation in the Forensics Laboratory Service Incident Response Team, which will respond and assist inspectors with collection and processing of major crime scenes and violent crimes.

Questioned Documents Unit

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A questionable document is examined by forensic specialist.

The Questioned Document Unit provides technical assistance to inspectors through document analysis. Lab experts determine a document’s authenticity by comparing "questioned" and "known" handwriting, typewriting, commercial printing, and other machine or mechanical impressions, analyzing paper and ink and restoring eradicated and obliterated impressions. In addition, they visualize indented handwriting impressions and can detect altered and counterfeit impressions. The unit also supports audio and video enhancement requests and in-house forensic photography services.

Fingerprint and AFIS Unit

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Scott Peters, forensic analyst, processes a piece of evidence to develop latent fingerprints for examination.


The Fingerprint Unit assists inspectors by identifying suspects who have handled items of evidence. The Fingerprint Unit interfaces with Automated Fingerprint Identification Systems (AFIS) to assist in matching latent prints with known offenders. These analysts can develop latent (invisible) prints on evidence and compare a latent print to a known fingerprint, palm print or footprint of suspects. Fingerprint analysts also assist inspectors by preparing charts demonstrating identifying features of "questioned" and "known" prints and testifying in court.

Physical Sciences Unit

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A questionable document is examined by forensic specialist.

The Physical Sciences Unit includes a Physical Evidence and a Chemistry section. These specialists conduct chemical analyses, perform physical examinations and comparisons of materials, process crime scenes, and train postal inspectors to better understand physical evidence.

There are a wide variety of materials that make their way into the labs of the Physical Sciences Unit. Many materials can become clues, such as bombs (debris or intact explosives), suspected arson accelerants, firearms (and possible serial number restorations), and items as seemingly inconsequential as tool marks, and shoe and tire impressions. Some of the smallest items can be the most challenging to handle (fibers, hair, adhesives, paint, paper, plastic, and rubber) but these trace evidence pieces can lead to large discoveries.

Analysts in the Chemistry section examine mailed materials suspected of being controlled substances. They use a variety of chemical techniques to determine a compound, including high-performance liquid chromatography, mass spectrophotometry, and gas chromatography.

Digital Evidence Unit

Computer circuit board inside a computer
Digital evidence

The Digital Evidence Unit experts are housed in 19 offices throughout the country to better allow them to support field inspectors on search warrants. The Digital Evidence Unit is responsible for the collection, preservation, and examination of computer digital evidence supporting the service’s investigations. Such evidence could come from anything from computers and phones to cameras and other digital media storage devices.