If people were really being abducted by aliens could convincing forensic evidence be collected from their person upon their return?

A California podiatrist, Roger Leir, claimed so. He claimed he had removed alien implants made of 'the same material as meteors' from patient's feet. Meteors are largely composed of common materials such as silicon, iron and aluminium. Critics suggested Leir had been removing particles of stone, metal, etc, which had become embedded in people's feet due to walking barefoot.

One would think so.  

Look at modern crime scene investigation: a hair or a drop of bodily fluid or some flesh captured under the victim's fingernails yields court admissible DNA evidence. 

For me, I will believe it was an "alien" when they find DNA that is composed of chains of nucleotides other than cytosine [C], guanine [G], adenine [A] thymine [T]), or uracil (U) [from RNA] of which all terrestrial life is made from.   

Implants found in the body are quite common. When they are removed, they are normally the size of a grain of rice. They are found to be made of the same material as meteorites and treated with a substance that stops them from being rejected by the body. A substance that we don't have and can't identify. There are several vids on YouTube, showing them being removed. People getting their leg or other parts of the body cut open for a joke is a daft way to think unless you are a denialist because they think we all have a great sense of humour and don't mind having our bodies slashed open just to pull a prank.

Jon, how come you don't have an implant or the old woman next door to you? How come they are found in people who claim to be abducted? How come they are not called foot implants? That is because they are found in the stomach area, arms, legs and even head? How come nobody feels a grain of rice size item enters their feet? Why do people only pick up these implants that are made of meteorite material and not a sharp stone or glass? How does it get through their shoes? Why is the body perfectly happy with them with no sign of rejection? How are these implants covered with a viscous chemical that we can't identify yet it stops the body from rejecting the implant. Your answer is completely improbable

The one thing that "validates" people being abducted by what they THINK are aliens is that the DESCRIPTIONS of the "ALIENS" match.  This was especially true before the "CLOSE ENCOUNTERS of the 3rd Kind" movie in 1977, that put the "Grey" alien in our public iconography.

If they were ALL lying, then there would be NO Matching descriptions.  If you put 50 people in a room with a pencil in paper and tell them to "invent" a space alien" for a movie you would get 50 different aliens.---We all know that.   Does this mean that people were really adducted by "aliens"? CERTIANLY NOT, but it strongly suggests they had the same experience and SAW the SAME thing----But why?

Assuming there are NO ALIENS, the best possibility is A Hoax.  But it is a hoax on a very large and expensive scale---only an organization affiliated with the GOVERNMENT could pull it off.---Again we must ask WHY?

The best answer would be a COVER UP of some secret weapons accident or unethical experiment that might cause public panic or scandal if leaked out---and requires that those possibly exposed to toxic, radioactive or biological agents be periodically tracked and examined.  Likely the CIA or NSA is doing the abductions, drugging the victims, and bringing them to mobile Labs for examinations.---The "Space Aliens" are "dummies" or "Animatronics"  present to confuse and frighten the drugged victims and make them reluctant to talk, should the amnesia effects of the drugs wear off.---And not be believed if they talk anyway.

---A stroke of genius, on the Government's part, but has a flaw in that they use the SAME dummy---resulting in MATCHING descriptions, lending both veracity to the reports and opening it up to logical analysis as we see here.----

This is not a "Conspiracy theory" as such theories start with the conclusion and evidence is "found" to back it up.  The above is a Logical Deduction as Sherlock Holmes is famous for.----And likely very close to the actual truth.

NOTE: any Valid theory MUST explain how the "Alien" descriptions before 1977 MATCH---If it does not do that  it is bogus.  Above we propose that all the victims saw the SAME style dummies. so they had a real experience. and the simplest argument is the GOVERNMENT is behind this for some reason.

You would think so, but those aliens really know how to sanitize a crime scene (or person). They don't leave any physical evidence. We shouldn't be surprised. If they are advanced enough to travel through intergalactic space getting rid of a little evidence would be child's play for them. 

[People are not really abducted by aliens. But I take we agree on that]

Answer is "it depends".

It is not like aliens had to be radioactive being sweating unknown chemicals or I don't know what.

So there is no known marker, for an non existing event. And no reason to believe that such a marker should exist.

But, well, obviously, if you find a probe made of ununennium up their butts, well, you'll have to at least wonder what it is, and how it end up here.

(Even then, it is no proof that it is alien. It can still be a secret operation from a hostile government. From Ockham's point of view, that is even still a better explanation. But, still, you would know that the abducted persons are not just imagining tales. Something that was not supposed to be possible happened to them)

Even with less extreme hypothesis. If you find trace of microorganism that looks unearthly on them... again, alone it proves nothing. But if you happen to find those on people that are telling that they were abducted by aliens, and should not have access to capability to engineer fake microorganism (I mean, if your witness are all russians microbiologist, on vacation in US, who claimed to have been abducted, there is still room for doubt).

But that is all hypothetical (I mean, in addition to your question being hypothetical from the start anyway). Maybe those imaginary aliens can just wear protective equipment to avoid letting trace. After all, they invented interstellar, faster than light, travel, plus the tech to avoid detection from all governments and universities on Earth. Maybe they also invented hazmat suits.

There won't ever be forensic evidence of a non existent event!

This question has nothing to do with either religion or spirituality. It belongs in either the science fiction, or mythology section.  The answer to it is, "No, it could not".