So why was the head of the lab's DNA on the evidence? He doesn't wear gloves? How did they know it was his?
Because people who work in labs have to handle the actual samples, so there's a slight chance of contamination by the technician's DNA. I don't know for sure, but it would make sense for lab workers who handle the actual physical samples to have their DNA profiles on hand at the lab for exclusionary purposes. These profiles of course would not go into a governmental database but would be kept on site as a working tool and most likely be deleted from their in-house system when that technician leaves employment. My recollection of Meehan's testimony was that there was a match from one sample to his DNA in the form of one skin cell but I don't remember him testifying that they took a sample from him at the time to test, so it seemed as though his profile was already available there to them. Yes, I'm certain he wore gloves. The comparison would have been for exclusionary purposes and his cell would not have presented as the actual sample under review. At any rate, a DNA lab technician's DNA on file at a lab would not go into any outside database.
You can probably find a fuller answer to your question by researching DNA lab procedures for technicians who handle samples.