OK, quick synopsis. Some bits of this may be out of order. Spoilers abound, obviously, so…
A man is about to be executed for the murder of a college student some years ago. At the last second, he is granted a reprieve. (Literally, they had to revive him.) His attorney had gotten a reprieve so that the DNA evidence against him could be reviewed again.
Catherine had worked the case years ago and so gets it again. Three college students had been raped and murdered and the man in question had been convicted of one of them. All of the victims were found the same way; hands bound with zip-ties and tied in a plastic trash bag. All of them had blue paint on one hand (important). The evidence had only connected him to one of the three killings.
Catherine sends some hair samples from the victim off to a federal lab to check for mitochondrial DNA; their own lab cannot test for this apparently.
Grissom, Sara and Nick get called to a trailer park where a 17 year old girl is missing. The girl’s father is outside, quite drunk, with blood on his shirt. Sara examines him while Grissom and Nick search the trailer and grounds. They find the door to the girl’s room has deadbolt locks which can be locked from the inside and its own refrigerator. They also find a towel or robe (couldn’t tell for sure) with blood on it and a karate gi with a black belt.
Searching a shed behind the trailer they find a hidden compartment with a large number of guns, including an automatic weapon.
Catherine is confronted by the parents of the murdered woman who want to know about the new DNA tests. Catherine is obviously upset but can’t tell them anything. She gets called away.
She is called to the college where they find another woman, killed the same way as the three 15 years ago. (Hands tied with zip-ties, stuffed in a trash bag, blue paint on hand.) Warrwick is assigned to help her. Catherine finds a bug and some black fibers in her hair. They wonder if this is a copycat killer.
The attorney for the convicted man confronts Catherine and accuses her of being biased against her client and says her client is obviously innocent since the murderer is still out there. Catherine says she only listens to the evidence.
(Through all of this we keep seeing the tests being run at the federal DNA lab.)
The father from the trailer doesn’t seem concerned about his missing daughter. The blood on his shirt is his but the blood on the robe is the daughter’s. They then discover the murdered woman from the college is the missing daughter, so everyone is now on the same case.
Grissom checks on the autopsy and finds that the woman has a cut on her hand; she fought back. (She was a karate black belt, remember?) There is a bit of glass in the cut and they are able to determine she got it after getting the paint on her hand.
Sara is able to determine that the black fibers from the murdered woman is from car upholstry but only that it is from a Chevy. The lab recovers a single, partial print from the trash bag.
The murdered woman’s car is located at the college and everyone goes there. The car is extremely clean; several of them comment that it is almost too clean. They cannot find any evidence in it. They learn what class the woman was going too and Warrick, who apparently went to this college, knows how to get to that class from where the car was found. He leads Catherine there.
Along the way, they cross a small bridge and he touches the railing, getting blue paint on his hand. They suddenly realize where they blue paint has come from. There is a water fountain nearby.
Everyone converges on the spot and they realize that the killer put the fresh paint on the the railing and waited for someone to touch it. When they went to the fountain to try to wash the paint off, he attacked them. Grissom comments that they never knew what the paint was for until then and asks how the copycat, if that is what they are dealing with, knew.
Warrick finds the woman’s backpack, id, keys, etc. in some trees. Catherine finds a tree with a bug on it like the one she found in the victims hair. Grissom says she fought back and got pushed into the tree. They also find a piece of glass on the ground near the tree. The light bulb over the fountain had been broken out, but this is different.
Back at the lab, they discover that the glass matches that from the woman’s hand and that it is from a pair of eyeglasses with a relatively mild perscription.
They also discover that the paint is oil-based and was mixed with motor oil to cause it to remain wet for a long time. Grissom finds some brush fibers in the paint.
Grissom and Catherine go to the school art department and talk to someone there. He claims not to know anything. Grissom says that he found bristles from a badger hair brush in the paint and the artist indicates that he also has one, but that they are easily obtained from the school bookstore. Grissom examines his glasses.
The report from the federal DNA lab comes back positive; there is a definite match. The execution is on again. Grissom theorizes that the man being executed was the copycat, not the original murderer.
The teams tries to find anyone who was at the college 15 years ago who is there now and find one match; a student then who has recently returned as a professor.
They question the professor, who turns out to be the same person they spoke to earlier. It is revealed that he painted pictures of the murder victims 15 years ago and also that he dated one of them; he even went out with her the night she was killed. Sara, Nick and Warrick examine his car, which turns out to be a Chevy with a black interior, but it is also immaculately clean and they cannot find anything. Also, his prints do not match the partial print from the trash bag. They have no evidence connecting him to the crimes and so let him go.
Grissom performs a spectral analysis on the paint from the hands of all four victims. Three of them match; two of the original murders and the one from the recent murder. The one from the woman who the man being executed killed is different. This means that he killed only that one woman and the other three were killed by someone else.
The original victim’s family asks Catherine to be with them at the execution. She goes and watches the execution, then leaves.
Grissom meets with Jim and, since they are both “off the clock”, they share a drink. Grissom says he likes his job because he can find the evidence that the criminal didn’t know they left, which means he is smarter than the criminal. He is afraid that this time he is dealing with someone smarter than he is.
The show ends, leaving the question open…
Hope this helps.