NCJ Number
137435
Journal
FBI Law Enforcement Bulletin Volume: 61 Issue: 6 Dated: (June 1992) Pages: 11-13
Date Published
1992
Length
3 pages
Annotation
The Federal Bureau of Investigation (FBI) has received requests to conduct forensic examinations of disposable blown film products, such as garbage bags, and it is hoped that bags obtained as evidence primarily in homicide or drug cases will be associated with a similar film product in the suspect's possession.
Abstract
Blown film is produced by converting resin pellets (polyethylene) to a melt which is then forced by an extruder through a ring-shaped die to form a continuous tube of plastic. As the melt exits the extruder, it is forced through a screen at high pressure which may accelerate debris and impurities through the screen to the die. The inflated tube is regulated for desired film gauge, collapsed by frames, and pulled through nib and idler rolls. In an ideal manufacturing environment, all possible film defects would be detected and eliminated. In reality, however, numerous occurrences impart class and unique individual characteristics that enhance forensic examinations. Such examinations, physical comparison, and matching of polyethylene plastic bags are conducted visually with the aid of transmitted light and low power magnification. In addition, industry research has developed a profilometer to measure caliper average, low point, high point, and profile of the polyethylene film. Special care is required to collect, preserve, and transmit the bags. The forensic examination of these bags for class and unique individual characteristics can provide criminal investigators with an additional scientific means of solving questions associated with plastic bags obtained as evidence in criminal cases. 10 endnotes and 1 figure