Can DNA be there from before?

Yes.

DNA can remain in a location from earlier contact and may still be detected later.

Biological material can persist on clothing, bedding, skin, and surfaces for varying periods of time. The length of time depends on factors such as the type of material, handling, movement, washing, and environmental conditions.

Because of this persistence, DNA detected in a sample may relate to prior contact rather than the alleged event. It may originate from earlier interactions, shared environments, or everyday handling.

DNA may also be transferred indirectly and remain in a location without direct contact occurring at the time of the incident. In some cases, biological material can move or be redistributed after it was first deposited.

Laboratory testing can identify DNA and sometimes link it to an individual, but it cannot determine when the DNA was left. It cannot distinguish between recent deposition and earlier presence.