Not so certain on the DNA; his need for publicity is what got him. He called one of the detectives on the case while he was still on the outside and asked him if floppy disks could be traced. Of course he detective said no. He then proceeded to mail a floppy disk with some info on it, source analysis traced the disk to the church he was working at, voila - captured BTK.
You are correct, he created the disk on his church computer and they got church name and “Dennis” there. Then they subpoenaed the daughter’s college medical samples. Her DNA direct matched victim semen etc.
I agree.....eventually they will always make a mistake that’s generally what gets them in the end. He is certainly one disgusting individual to say the least. But in reality just another sadistic serial killer.