Dr. Clark Murray is a forensic pathologist who works in NYC and makes his first appearance in A Death in the Family. He's also someone that Castle has consulted with when writing his novels. Dr. Murray jokes with Castle, saying that he usually calls to ask what happens if you put a head in a microwave. Castle states this one is a little less made-up. He continues on stating that this victim is the mother of the detective he's been following around and that the case has been cold for ten years. Castle feels that since he's the best forensic pathologist in the city, that Dr. Murray could catch something that was missed. The doctor tells Castle the odds of finding anyone's killer after ten years is astronomical. Castle states he understands but would appreciate it if he took a look at the case anyway.
Dr. Murray returns to Castle's loft, several days later and tells him that the original M.E. concluded that the stab wounds were random. Dr. Murray points out that one of the wounds was a low-angle thrust to the kidney. The size of the wound indicates that the knife was twisted and that she went into immediate shock. Other wounds indicate that they were delivered after she was immobilized and on the ground and were just for show. The wound to her kidney was the one that killed her. Castle states that this is sounding less like a random killing and more like a targeted murder. Dr. Murray continues to explain that on a hunch he checked the city M.E files to see if this was an isolated incident and he found three other stabbings around that time. The M.E. working the case dismissed as random. Castle asks him if they were random. The doctor asks him if he's sure he wants to know.
Dr. Murray appears for a second time when arrives at the 12th with Lanie and is introduced to Beckett in Sucker Punch. She tells Beckett that he's a forensic pathologist and that she asked him to consult on the Coonan murder. In the conference room, Dr. Murray points out to Beckett the rectangular bruising around the wounds on Coonan. The wounds were caused by the hilt of the knife striking with enough force to compress the skin. Beckett points out that the result is the injuries penetrate deeper than the actual length of the blade. Dr. Murray continues to explain that the killer has also honed the blade so fine, that it's brittle enough for bits to break when it strikes bone. This is why slivers of the blade were found inside both of this victims and that those slivers come from the same murder weapon. Beckett asks how many victims has he killed and Lanie answers five that we know of. Dr. Murray says that the killer is a professional and some with extensive military training. Dr. Murray contines on that he used tomographic reconstruction of Coonan's wounds and he generated a 3D model of the blade used. He pulls it out of a plastic bag and hands it to Beckett. He points out that it's a special operations group knife and it was the kinds favored by special forces in the Gulf War I. The killer uses a single blow and uses the other wounds to camouflage the skill with which the initial stoke was delivered. Dr. Murray states it's the very same method and the very same weapon that the killer employed ten years ago. Dr. Murray concludes that there is no doubt in his mind that Coonan was killed by the same man who murdered her mother.