That's what I read yesterday. Without 13 matches, the "supposed perp" is excluded. It is not him.
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Let me try this again:
1. An exclusion:
A. They take the sample from the evidence and identify 13 markers on it.
B. They take the sample from the suspect and compare to the 13 markers from them.
C. If the 13 markers do not all match the person is excluded and could not have left the DNA.
2. A match:
A. They take the sample from the evidence and identify 13 markers on it.
B. They take the sample from the suspect and compare to the 13 markers from them.
C. If the markers all match the suspect is matched to the evidence and with a very high probability left the DNA in evidence.
3. A partial match:
A. They take the sample from the evidence and identify as many markers as they can on it, but it is less than 13.
B. They take the sample from the suspect and compare it to the LESS THAN 13 markers from the evidence.
C. If the LESS THAN 13 markers all are the same as the suspects suspects equivalent markers, then you have an inconclusive result or what some are now trying to pass off as a partial match.
The example I saw was between brothers who were both at the scene of the crime AND I think it was a rape case. Obviously, they're not going to snitch on each other. One brother had 12. The other brother had 13. DNA became the scientific snitch!!