When you touch a device, you leave 'biotraces' on it. This can be like the character ID being stored in an array on the device. Maybe associated with a modifier representing how strong the biotraces are (recently showered, fewer biotraces, wearing gloves, fewer biotraces, and so on) and a timestamp.
Using a tool someone can use forensics to compare a biosample (a person, body part, dead body, a blood sample) and an item and see if there is a match. If there is a match they will try and gauge the time frame. Chances of finding a match and the accuracy of the estimated time frame will vary based on the person's skill.
To give it some weight, the tool will display the result of the test on the display. This way the test can be run again and again in front of those wanting to know an demanding proof and they can read the results them selves even if they can't perform the test.
