As Iron Mike says, you're close to or over the line into classified material on what MI5 uses for identification. I have a relative who did not work for the CIA. His parents were taken by bus to a secret graduation. My guess is his fingerprints were not in NCIC, unlike most Federal employees. And this is someone who would have been known within the intelligence community as someone who worked for the CIA.
Identifying a dead body is a lot tougher than most people think. Most bodies are identified by identification with the body. Photo ID is becoming somewhat common. Fingerprints can be good for quite a while, but that assumes someone is in the data bank. I am because of various jobs I've had. My wife is not. When a medical examiner runs prints, there's a significant likelihood of it not coming back. DNA is very rare to find in databases. The two biggest I know of that are available to medical examiners are criminals and missing people. A lot of time now with missing people, the police try to get DNA from a relative (parent, sibling, or child). DNA hits are very unusual and take a couple of months to come back to the medical examiner.
Usually if the fingerprints don't work, the medical examiner or police will circulate the photo of the individual (which may be retouched to make it look more lifelike) and a description of the clothing. At this point, the odds of the body being identified are becoming less and less. The photo will be circulated to compare with missing person files, but beyond that, there's not much you can do.
Anybody who is at all undercover is a suspicious person. That's how they survive. Dead bodies in the neighborhood are always going to make them nervous.
However, if someone is leaving the body as a warning to the agent, my guess the person is going to leave a way for the agent to figure it out.
Jim