Su W.J, Michael Tay Ming Kiong
International Association of Forensic Sciences 17th Triennial Meeting,
Hong Kong, 21-26 August 2005. (oral presentation)
Background: Plastic strapping is commonly used for strapping products ranging from light cardboard cartons to heavy loads such as pallets of bricks or bundles of pipes. Besides bundling and unitizing items, the straps reinforce cartons and ensure secure packaging during shipping and storage. This paper presents a case study of two strapped cardboard cartons containing luxury watches which were couriered overseas from the manufacturer to the retailer. The cartons cleared the Customs and arrived at their destination but on opening, both cartons were found to empty. It was not known whether the watches were stolen before packing or during transit. The investigator submitted for forensic examination two questioned cartons, a questioned white security seal holding together four lengths of yellow plastic straps, and a control sample consisting of a white security seal holding together four lengths of yellow plastic straps. The two cartons were originally strapped by the 4 lengths of questioned straps.
Methods and results: The two white security seals were a two-piece tamper-evident type with unique markings for use with plastic strapping around cartons. They were intact and undisturbed, indicating they had not been tampered with. The cartons were tamper-resistant and it was not possible to access the contents from the sides without inflicting obvious damages on the cartons. The four lengths of straps were firmly held, extending from the four sides of each security seal. These four lengths belonged to two straps crossing each other at right angles in the security seal, binding the cartons such that the straps could not be slipped off the cartons. The plastic straps had an embossed surface with repetitive diamond motifs. The questioned and control straps were found to be made of polypropylene and poly (ethylene propylene diene). The two heat-sealed joints on the questioned straps were microscopically examined and evidence of separation of straps (peeling) in the joints were observed; material had been ripped out from the straps, causing tears, splits and fibrillation in the strap material. Poly (ethyl cyanoacrylate) adhesive was found in the seams of the two joints and on nearby surfaces.
The control straps had a damaged joint and an undamaged joint. These two joints did not have poly (ethyl cyanoacrylate) adhesive on nearby strap surfaces. The damaged joint had been subjected to peeling, which separated off the mating length of strap, leaving behind a whitish-yellow rectangular patch of residual fibrous material from the peeled off strap. Both the damaged and the undamaged joints had relatively neat and clean edges with melted yellow material from the straps fused together. Some melted yellow strap material had extruded from the sides of the joints. The binding materials in the two joints were made of the same material as the yellow straps, indicating that the joints in the control straps were heat-seal joints made by partially melting, and fusing two tensioned straps together with pressure.
Conclusion: Stereomicroscopy, examination of damages and materials analyses indicated that the heat-seal joints on the questioned plastic straps had been tampered with; the joints had been peeled apart and cyanoacrylate adhesive was used to re-join the straps and conceal the theft.