An apparatus and method for purifying a forensic sample using an automated extraction and purification system includes optical tweezers; an input channel through which the sample is introduced; a chamber which receives the sample from the input channel; a collection channel through which selected particles of the sample are removed; and an output through which unselected particles of the sample are removed. At least one buffer input channel is provided. The input channel may allow sedimentation of the sample into the chamber by gravity. In another arrangement, the system includes an optical trapping system; a first channel through which the sample is introduced; a second channel through which buffer is introduced; wherein the optical tweezers are used to move selected particles of the sample from the first channel to the second channel. The selected particles may be sperm. The optical tweezers preferably utilize holographic optical trapping.