What if DNA or other indirect evidence point to a person being guilty, but there are no probative witnesses?
DNA (and other forensic) evidence can be used by the judge to challenge or support actual probative witness testimony, but cannot count as one of the "two or more witnesses" (Deut. 19:15) for the purpose of establishing guilt. If there are no probative witnesses, the case must be dropped. DNA cannot itself be a probative witness, because the probative witnesses must be able to throw the first stones (or the modern equivalent): Deut. 17:6-7, John 8:7.
Some people have suggested that a "DNA technician" might act as the "stone-throwing" witness. But a stone-throwing witness has to be so certain of the guilt of the accused that he/she is willing to risk murdering an innocent man if he/she is wrong. DNA is indirect (sometimes called "circumstantial") evidence. DNA evidence can be planted, and it often can only show that someone, or a near relative (such as a brother), might be implicated. The technician must be able to testify with utter certainty that the DNA could not have been planted. And the technician must be able to convince the judge of this, and be able to back up this accusation by actually throwing the first stone.
That doesn't mean that everyone in a community is required to trust a person who is under suspicion -- just that they aren't allowed to use force against him in retribution, according to Biblical law.
