According to all the news reports I've read, the police and/or the FBI have a DNA match, his confession, several murdered victims' items found in his back yard, and his "electronic fingerprints" on a floppy disk he mailed to them. That's just the stuff I can remember off the top of my head.
Some details about that floppy disk:
Rader typed something at his church and saved it on the floppy disk, but forgot to erase at least one file/folder on it. The folder's name was the same as the name of this Lutheran church. Last Friday, the police went to this church and asked the pastor if Rader had recently used one of their computers. The pastor said yes, then pointed to one of their computers. This computer was a match for whatever was on that floppy disk.
Also, the police are most likely eager to know more about the gun Rader used to make his victims submit to being tied up. News reports say he had a gun when he killed the lady who had 3 kids at home. (Her name was Shirley-something and the kids were locked in the closet). One of those kids had let Rader in the front door and the kid said he had a gun.
I'm thinking that if the police can find out more about Rader's gun, they might find that he was the Interstate 70 "white, slender male" who killed all those women in the 1990s.
Thank you for the information. The evidence is pretty strong against this guy. How devious to be living such extremes of a double-life....