Advanced Techniques for Developing Latent Fingerprints

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Presentation transcript:

Advanced Techniques for Developing Latent Fingerprints STEM

Ninhydrin: Discovered for fingerprints in the 1970s by a university scientist who was working on a process that stains protein tissue sections. After an accident he found that it made his latent fingerprints visible.

Major Advantage : It can be applied to large surfaces by using a spray bottle.

Major Disadvantage It is toxic and should be used in well ventilated areas.

How does it work? Ninhydrin reacts with the amino acids present in the perspiration on the print, turning the print purple.

The reaction:

Iodine: Up until the 1970s Iodine fuming was one of the classic/main methods to visualize latent fingerprints. This method is now seldom used.

Iodine: Iodine is one of the few chemicals that sublimate (change phases from solid straight to gas)

Major Disadvantage It is toxic and should be used in well ventilated areas.

How does it work? Keeping a print on paper in a closed container, Iodine will react with the oil in the print resulting in a brownish print to develop.

Iodine: The print will fade quickly if it is not fixed. This is done with a solution of Calcium Chloride and Potassium Bromide in water. The print will then last a few weeks.

Physical Developer (silver nitrate AgNO3) -used on porous articles that might have been wet at one time. - can be used after iodine fuming and ninhydrin

Disadvantages - will destroy any traces of protein from an object’s surface (hence, no DNA collection from the print)

Super Glue: Discovered accidentally by a civilian forensic scientist at the U.S. Army Crime Laboratory in Japan.

Super Glue: Contains Cyanoacrylate which is the ingredient that combines with the print.

Major advantage : You can use it to develop prints on materials which no other method will work. ex. plastic

Super Glue: Powders are unsuitable for many types of plastic surfaces. The powder tends to smear over the plastic as if it were oily.

Another Advantage It can develop “thin Prints” - prints which only a trace amount of material is transferred from the finger to the print. Super Glue can be done after dusting is tried.

Fuming Tank

Other Development methods Magna Brush: a magnetic device which allows you to dust a print with iron dust. Amido Black: a chemical which enhances faint blood patterns. Ardrox & Basic Yellow: dyes which absorbs into super glued prints. (helps with photographing the prints) Crystal Violet: Used on the sticky side of tape after a print is lifted to help visualize

Other Development methods DFO: 1,8,diazafluoren-9-onesimilar uses as ninhydrin and amido black. Indanediones: similar to DFO and ninhydrin. Leuco Crystal Violet: stain that enhances bloody prints Ray: A mix of Rhodamine 6G, Ardrox, and Basic Yellow. Put on prints to help visualize.

Other Development methods Redwop/Greenwop: Fluorescent powders which can be enhanced by high energy lamps. Small Particle Solution: a suspension of molybdenum disulfide that can be sprayed on porous surfaces. Stickyside Powder: a product of Japan. Made to be applied to the sticky side of tape. Sudan Black: An industrial dye that is absorbed into the print oils.