Study on traces left on a mechanical lock picked by a 3D printed key in toolmarks examination

Zhen Wang; Hao Zhou; Chao Ye; Changjiang Song; Taiqi Zang

doi:10.1016/j.forsciint.2020.110514

Study on traces left on a mechanical lock picked by a 3D printed key in toolmarks examination

Forensic Sci Int. 2020 Dec:317:110514. doi: 10.1016/j.forsciint.2020.110514. Epub 2020 Sep 18.

Authors

Zhen Wang¹, Hao Zhou², Chao Ye³, Changjiang Song⁴, Taiqi Zang²

Affiliations

¹ Department of Trace Examination, Criminal Investigation Police University of China, Shenyang, China. Electronic address: wangyuchena9@163.com.
² Department of Trace Examination, Criminal Investigation Police University of China, Shenyang, China.
³ Gongbei Public Security Bureau, Zhuhai, China.
⁴ Institute of Intelligent Manufacturing Heilongjiang Academy of Sciences, Haerbin, China.

PMID: 33096397
DOI: 10.1016/j.forsciint.2020.110514

Abstract

The three-dimensional (3D) printed key is a key that can be manufactured from its virtual model by means of a 3D printer. This research focuses on the picking feasibilities and traces that can be observed and exploited from a forensic point of view after the picking of such type of keys. In this paper, 40 printed keys were manufactured using three different polymer materials (white resin, white nylon powder and black ABS). All the experiments were carried out under controlled conditions to allow the collections of data and traces produced by the picking. Of the 40 prints, only 38 picked the locks and the total picking ratio was 95 percent, meaning that a 3D printed key using polymer materials can be used to pick a lock. Elements of lock - pins and keyways - appeared to carry polymer materials (flakes or pieces) transferred from the prints during picking process. Additional, characteristic marks of a 3D printed key on the surface of pins was identical to those of an original key, but not similar to those of other picking tools. Indeed, this method could not create more marks on the bits of an original key while striations were left by the picking method using a duplicated key. Besides, FT-IR was a useful method of analyzing the type of polymer material used. When receiving original keys and a lock suspected to be picked in a crime scene, the toolmark examiners can quickly determine whether or not the lock was picked by a 3D printed key based on the examination results of these traces.

Keywords: Fourier transform infrared spectroscopy; Picking mark; Polymer materials; Three dimension printing technology.