The Reflected Ultraviolet Imaging System (RUVIS) was first made available to law enforcement agencies more than a decade ago and is now in use throughout the U.S.A. by Federal, state and municipal agencies, and it has become a valuable aid to governments around the world.
RUVIS derives its uniqueness from the fact that this handheld device permits investigators to actually see latent fingerprints on nonporous surfaces BEFORE any attempt is made to develop them using the traditional methods discussed in previous articles in this series.
The basic theory behind RUVIS is the fact that certain surfaces reflect Shortwave Ultraviolet light, which in itself is invisible. But a RUVIS device changes this.
RUVIS is a two-part system consisting of a portable shortwave UV light and the handheld RUVIS device.
Here’s the basic theory of RUVIS operation:
1. Most nonporous surfaces will either reflect UV light or will absorb it so that no light is reflected. Much depends on the angle that the UV light strikes the surface.
2. The RUVIS device utilizes a specially-constructed lens designed to pass UV light. Most commercially- made camera lenses have features that block UV light, because it interferes with the color balance of the resultant photographs.
3. The RUVIS device is equipped with a “bandpass filter” located behind the lens assembly that blocks all but shortwave UV light—including ambient light in the scene. This permits use in bright sunlight or total darkness. Only the reflected UV light passes through electronic circuitry that amplifies the weak UV light and converts it to visible light—so that it can be seen.
4. Depending on the color and physical nature of the surface being examined, and the angle and distance from the surface that the UV light is positioned, either the background or the moisture of a latent print is seen through the RUVIS device.
5. In the case where the surface is reflecting the light, any latent prints on this surface will absorb the light. The result is that the background will appear as a lighter color on the RUVIS viewing screen while the ridge structure of the latent prints will appear dark in color.
6. A slight change in position will sometimes cause the opposite to occur: the background will be dark and the ridges will be light in color.
Some RUVIS devices permit the direct connection of a camera to the viewer permitting photos of the latent prints to be taken before any attempt is made to develop and lift these prints.
Using a RUVIS device has many benefits both at the crime scene and in the crime lab. Since the user can actually see what is present, he can eliminate the time taken to develop smudges and smears, which have no apparent value. The RUVIS operator can direct his attention to only those prints that may have forensic value.
But another advantage is that recent discoveries make it possible to recover DNA evidence from latent prints, so those CSIs who are collecting DNA evidence can be directed to the smudges and smears instead of collecting useable latents.
Overall, RUVIS saves considerable time that is usually spent in processing an entire crime scene for latent prints.