This technique can be used on samples taken from guns, steering wheels, cell phones, glass, plastic, wood, cloth, fabric, etc. While you might be tempted to take samples from every single surface and object at a crime scene, you have to be smart about what you’re doing. Focus on the places a suspect is likely to have touched.

When you take your samples you can either use the cut method or the swab method. The cut method allows you to take samples from soft surfaces like cloth, fabric, etc. This method works well for items like shirt collars where there is likely to be sweat and skin cells. The swab method is used on hard surfaces like glass, plastic, wood, etc. As you can see from the photos, you can use this method to swab the trigger, hammer, or grip of a gun or the surface of a cell phone. Getting DNA evidence from guns and cell phones can be crucial to your case, since it can be very difficult to get fingerprints from these objects.

From: Touch DNA by Dick Warrington in Who Says You Can't Do That?