Metal detection: the crime scene's best kept secret

FBI Law Enforcement Bulletin,The, Feb, 1995 by Richard K. Graham

It has been said that one person's trash is another's treasure. Nowhere is this adage more true than in the law enforcement setting.

Fragments of metal that most people would disregard can be, quite literally, crime scene treasures to investigators. These pieces of evidence become forensic gems in the hands of skilled examiners and constitute a veritable bonanza for trained law enforcement officers who understand the value of physical evidence. In other words, small metallic fragments can be the "stuff" that makes convictions.

This article reaffirms the importance of the one investigative tool - a quality metal detector - that can locate hidden metallic crime scene treasures perhaps better than any other. In the hands of a skilled investigator, the metal detector represents an indispensable weapon in law enforcement's arsenal. Yet, all too often, metal detection seems to be the crime scene's best kept secret.

CASE STUDY

A shootout between a police officer and a subject left the officer in serious condition with a gunshot wound to the abdomen. The officer had responded to a silent alarm and, finding the door of the business ajar, entered the building to initiate a search. He later reported that as he stepped out the back door of the building, he heard movement in the bushes to his left, but could not see anyone because it was a moonless evening and visibility was limited.

As the officer turned in the direction of the noise, he announced his identity. Instantly, two shots were fired in rapid succession from the subject's hiding place in the bushes; one projectile passed through the officer. According to the officer's account, he proceeded to move away from the building after being struck and, after four or five steps, fired twice into the bushes. He subsequently collapsed in a grassy area 30 feet from the door. Backup units responding to the scene took the subject into custody.

The subject's story completely contradicted that of the officer. The subject assured the arresting officers that he went to the building in question to speak with the owner. As he approached the building, he heard someone exit the back door. He then took cover in the bushes at the rear of the building. Without warning, the person exiting the building turned and fired at least two rounds in his general direction. In an effort to preserve his own life, the subject returned fire and then observed the other person stumble and fall to the ground.

The officer's bullets struck the wooden frame of one of the building's windows, so the points of impact were readily apparent. Established trajectories placed the officer 15 feet from the door when he fired his shots, supporting his claim that he had fired only after moving four or five steps away from the building. This reconstruction helped to establish the veracity of the officer's statement. Yet, it did not totally disprove the subject's story or verify the sequence of the shots.

Only the bullet that had passed through the officer could establish who shot first. If that bullet was found close to the side of the building, it would support the officer's statement that he was fired upon as soon as he exited the building. On the other hand, the further away from the building the bullet was found, the more credible the subject's story that he had returned fire only as the officer moved away from the door.

The police department called a metal detection/crime scene specialist to the scene. Following a preliminary survey of the scene, tests determined the conductivity of the 9mm bullet being sought. The metal detector consistently gave the same reading (signature) each time the searchcoil (antenna) passed over the test target. Additional tests indicated that the slug in question would remain intact and that the copper jacket would not separate from the lead core after passing through a human body.

Knowing the test bullet's signature, the crime scene specialist initiated a systematic and exhaustive search in an effort to verify or discredit the officer's statement. Metallic items unrelated to the shooting incident littered the search area. The operator ignored all metal signals until the detector located and reported a target item bearing the same characteristics as the test bullet.

The metal detector identified a single target with the same signature as the test bullet from among numerous other metallic targets in the search area. This fact alone was quite remarkable, but the metal detector provided even more critical information. The machine electronically pinpointed the target, placing the bullet within a circle approximately the size of a U.S. half dollar very close to the side of the building. Next, the detector signaled that the target rested just below the ground's surface, less than an inch deep.

With this information, investigators carefully probed the area and found a mushroomed 9mm copper-jacketed projectile. They measured and photographed the bullet in place, then carefully recovered and maintained it as evidence. Subsequent forensic examination of the bullet located fibers consistent with the officer's shirt.