Barbara, there aren't "matches" in DNA comparisons because in order to have any absolute match every marker on every allele would have to be compared. Forensic science doesn't do that.
One sample with markers in only certain areas of the DNA strand are compared to the same areas of the DNA strand in other samples.
If the markers are consistently in the same areas on the compared samples the likelihood that the DNA is from the same person is extremely high. Not many (if any persons) on earth are thought to have the same arrangement of markers at the same areas.
If a sample from the crime scene is weak and some markers are missing, the samples can still be determined to be consistent or not-consistent.
As an example only, say the nail clippings sample is examined at 10 areas, and markers are missing at areas 5, 6, 7, 10 but present at areas 1,2,3,4,8, 9. We don't know if the markers are missing because it's a weak sample or because markers don't exist at those areas in that person's DNA.
The suspect's DNA sample has markers at 5,6,7, but is missing markers at 1, 2, and 3.
The comparison is inconsistent and can't be a match because the comparison shows 1,2,3 cannot match.
Another suspect's DNA sample has no markers at 5,6,7, either but has markers at 1,2,3,4,8, 9, 10. This sample is consistent with the crime scene DNA and can't be ruled out because the crime scene DNA is weak & incomplete.