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The simplest way to fail a swab test is contamination of the sample. Eating something too soon before the test will do the trick.

Though what he really wants is the DNA of another human rather than a sample that comes back as beef cattle. These days there's an app for that, but in 2000 he'd probably have had to find a suitable bar to get himself a mouthful of human DNA sample*.

It's definitely the sort of thing a young man in trouble in the period would be told by his mates would work.

*If you don't know what I mean, ask your mum. No, I mean, no, don't ask your mum!

Step 1:

Line his mouth with something to keep the swab from hitting his actual tissue. It would help if he knew if it would be a cheek swab or a palate swab. A retainer would work on the latter. The former is a bit harder, but not impossible. Think flesh colored cloth. Or bite wings used to hold the teeth in place prior to dental x-rays. Or a cutup dental dam (or condom) carefully placed in the mouth.

Step 2:

Put someone else's salvia into his mouth. The easiest way to do this without asking for help, would be to find someone's abandoned (but recently used) plastic water bottle with a couple sips left in it. There would be plenty of backwash.

Step 3:

Put in the blocking material. Sip the remaining water and hold in the mouth as long as possible. Don't swallow at all. Let excess water drip down the throat or spit it out. It would not be unreasonable for someone to sip water just before getting swabbed, since opening a dry mouth while someone pokes around in there is uncomfortable. He'd have to time it well.

Will this work?

Maybe.

There are 3 basic ways to collect DNA for testing: Saliva (requiring a fair amount; it can be done with far less, but not reliably), blood, and cells from the inside of the mouth, usually the cheek. (There are other methods such as from dead bodies, bone marrow, forensic from hair, dried spit, etc, and from amniotic fluid, but none of these are relevant in this case.)

I think it would be hard to eliminate his own DNA from the sample. But probably easy to contaminate the sample with someone else's.

But given that you're looking for what your character thinks will work (or is his best chance at working), this is it.

Hold something radioactive, to any degree, in or near his mouth for some amount of time at any point prior to the test.

"Radiation alters DNA" is a trope beyond question or examination for most people, and this was also the case in 2000. Especially given the weak understanding most people have about radiation and radioactivity there are a lot of things Joe might see on some blog and try out.

Pressing his face against a running microwave for a few hours? Worth it, to avoid prison. Eating lots of bananas? Sure! That's especially helpful if Joe is really set on coating his mouth with something (bananas are easy to mash up).

It won't work, of course. But it's plausible that someone like Joe might find information pointing to such a solution, or might assemble this plan from information he's able to run across on the internet. The idea being "it's still my DNA, but different from my actual DNA".

Joe burgles a blood bank before he commits the crime (“burglary or deception is OK”). At the scene of the crime he spills plenty of stolen blood. The swabs taken from the scene of crime will contain far more DNA from random blood donors than from Joe, so when the forensics people amplify whatever markers they were using in 2000, Joe-derived template DNA will be out-competed in their PCR reaction by template from random blood donors. The forensics people will therefore have nothing to connect Joe to the scene of the crime.

By the year 2000, they probably weren't relying on Southern blots any more, but that shouldn't make any difference. If they do run a Southern blot (labeled DNA amplified from the crime scene probing a blot of Joe's DNA?), it's unlikely to hybridize more strongly to Joe's blot than to their control blots. If they sequence their crime-scene amplicon, it's not going to match the corresponding amplicon direct from Joe since Joe's signal in the crime-scene swab is swamped by the random blood donors' signals.

Other plausible sources of decoy DNA apart from burgling a blood bank? He could wander round a hospital in a borrowed white coat, and exfiltrate some fresh clinical waste from somewhere between operating theater and incinerator. Blood from a butcher's shop would be OK as the decoy if the forensics lab's PCR primers bind to sites that are conserved between humans and sheep/cattle. I don't know if this is the case (or was in 2000), but the primers must obviously have targets that are non-variable within the human population (they flank the variables regions), so perhaps it would work...

See the episode of South Park (Season 21 Ep 3) where Randy wants his DNA sample to be that of a native American, and when the 23andme people come knocking on the door because of an inconsistency in his first sample he tells them to wait a minute and runs around South Park to find the Indian and gives him a deep French kiss to then run back to the people and give them a corrupted sample. Hope this helped.

I'm assuming that there's some fictional textbook, far-fetched (potentially farcical in complexity) answer with a reasonable success rate which involves lining the mouth with plastic/wax and covering with another sample. However, with the given premise that Joe isn't an expert (and may not ask an expert) I'd find it more feasible to have a "best guess" solution from Joe. A solution however that could - even on the periphery of probability work.

Joe's Reasoning

So "being Joe" for a moment:

1. I must provide a sample garnered from another human being; showing up on the test as "feline" would be an evident dodge and is probably as likely in resulting in his arrest as a positive match.


2. Preferably I would want to provide a sample from someone who is the same gender and race as me. It is most likely that visual observations would be taken by the testers when the sample is conducted (in part to thwart this type of evasion); if I show up as "White, Female" and I'm a Afro-Caribbean male then that's going to be a dead giveaway and an evident dodge.


3. It would be less than desirable to simple contaminate/sully the sample garnered; again this is likely to result in a re-test and arrest.

Method 1

Given those lines of reasoning, I (Joe) would visit a gay bar and pick up a man who happens to be the same race as me. (Being 2000, the general populous isn't as open minded, but it is legal and I would know where to go, even if I didn't frequent them myself). I would try to do this on the evening before the test day, then put effort in to ensure he stays the night and doesn't slip out a long time before the test; make him some bacon and eggs, suggest he stays in bed a while, etc. As close to the test as possible (assuming it's a home-visit?), I'd passionately kiss my new partner (however abhorrent I might find it; it's possible I'm averse to members of my own sex in that way).

Now I appreciate that it's unlikely this method would work, however as you request it's not the success; it's the plausibility; access to materials; non expert-info. To me (Joe), it's a plausible attempt at dodging the test that I could have engineered myself. It's also a touch dramatic that I'm willing to engage a sexual partner of my own sex if I've never done that before, in order to overcome this challenge.

Method 2

Further research on this (yet not beyond the potential realms of Joe's reasoning; something he could garner easily from rumour), one of the main ways to dodge a test is to simply have someone else take the swab:
https://www.alphabiolabs.co.uk/learning-centre/can-someone-cheat-a-dna-test-2/

Now whilst Joe can't (them knowingly) involve anyone else, a higher chance of success may be appreciated if Joe disappears off with the swab in his hand for a moment, to take the sample from his still-sleeping partner (if the test was a home visit, early in the morning - something he would know in advance). NB. Evidently the officers conducting the test would have not followed "textbook regulation" by allowing Joe to leave their sight with the swab, but then - it's first thing in the morning - one of the officers is still hung over, and the other is a trainee! - I'm sure this could be explained off somehow.

Method 3

An alternate method 2, bit wacky but follows the rules; Joe previously worked as a magician's assistant whilst taking a gap year from university, and learned sleight of hand. He takes a swab of his sleeping partner before the officers arrive and switches it with the test swab.

What about a late identity-theft attack?
Joe may switch the samples on their way to the lab. He can figure someway to replace the tag labels of a few samples including his own. This way the case would end up with a suspect - definitely not Joe - who will be jailed and close the case for good.

Fooling the test is an utterly stupid idea to begin with

If you fool the test insofar as the result will be unusable, you will be asked to do it again. If the result is again unusable, you are highly suspect (probably after the first time already, anyway).

If you fool the test insofar as to show someone else's DNA, you are likely to be caught because there's a good chance the other person is undergoing, or will (at some undetermined point in the future) be undergoing the same test.

Also, whatever crimes the other person has already committed or will commit, you will be linked to them. Also, it's a felony to cheat on the test (whereas not doing it isn't).

Not complying is a viable (although tedious) option. I'm talking out of experience because I've been in that exact situation in 2000. Well not the exact situation, as I didn't commit the crime. But close enough anyway.

If you are in a place like, I don't know, China (?) then you are probably out of luck, but the question says Central Europe.

Central Europe means police asks and you say "no". Per Article 11, European Convention No. 5 (which is legally binding in all states), this means you are innocent unless police can prove something different. They can't, unless there is a witness or other evidence (obviously there isn't or they wouldn't do a mass screening) or unless you comply. So well, don't comply. "Doctor, it hurts when I do this. -- Don't do it."

The Convention 5 is fundamentally legally binding in all European states (and even some non-European ones) since early/mid/late 1951 / early 1952, depending which state exactly it is and on how fast the respective government was at declaring so.

The mere fact that police is trying to pervert the legal system to something which is similar to what we had in the Third Reich (proof of innocence instead of proof of guilt) is reason enough. By complying you give up your fundamental rights and subvert the system that is meant to protect you and other citizens from haphazard persecution. This should be reason enough for anyone to say "No". Unluckily, that's not the case. People take liberty as granted, but are not willing to make sacrifices to defend it.

Of course, being innocent (in real and by the law) doesn't mean you will be treated as innocent. Police tries to argue you into complying -- you have the chance to prove your innocence (which is really perverse because you have no need to prove your innocence, they need to prove your guilt). You say no.

Police keeps telling you there's only so-and-so-few suspects remaining, and then that there's only a handful remaining and you had better comply because they're already closing in on you anyway. You get letters, you get phone calls. One after one, they bully every non-complier into submission with this procedure. You say no.

Police starts showing up in your neighbourhood and at your workplace (yes I am not joking), doing what they can do to allege you are a culprit without explicitly saying it. They poke in every hole, try to find something, anything, whatever. They don't.

You file a complaint. Police says they never showed up, but if they did, then they'd be careful not to allege anything. Well, that means those people who told me police made allegations to them probably made this up. Funny how my neighbour knew I didn't do the test in the first place, he must be a psychic.

So, finally, after filing a complaint, you never hear of it again. Seriously, that's it. End of story.

17 years later, the guy who did it has died of old age, and his daughter finds body parts in some barrel in his cellar or garage (or whereever it was). It's in the newspapers, but you never hear as much as an excuse from police for having been falsely accused.

But whatever, as long as you never hear of them again, what do you care.

Chew hair.

Joe would feasibly have seen TV or movies where a strand of hair is used to identify someone.

He thinks therefore that it can also be used to be a source of alternate/confusing DNA and can pinch a strand from a co-worker's jacket.

Joe may consider to send someone else with his ID to the hospital where the test samples are taken. The medical personnel usually does not question someone's identity when showing the valid invitation for sample taking and also they do not have sufficient experience of an ID check.