Plastic bags can play a key role in forensic investigations because they are often present as evidence material at crime scenes. Important evidence issues can include whether the recovered garbage bag is part of a roll found at a suspect's home or whether bags found at different locations came from the same roll. Plastic garbage bags are made from high-density or low-density polyethylene and can show, depending on the manufacturing process, the following defects: tiger stripes, pigment bands, surface scratches, "fisheyes," arrowheads, and extrusion lines. The extrusion lines play an important role in the comparison and subsequent linking of plastic bags. In the current study, high-resolution 3D measurements of the bag surface were performed with a laser profilometer, which allows for a measurement of the surface topography with a high resolution in all directions. Optical examination of extrusion lines in low-density polyethylene bags show that they continue over substantial distance; however, the obtained 3D profiles have a correlation length on a much smaller length scale. This may bring a substantial added value to the linking of the end of one bag to the beginning of the subsequent bag. For high-density bags, adjacent strips can be linked by using surface scratches. A link between distant bags on a roll can be made if the surface scratches continue over the bags being examined. 17 figures and 6 references