This is scary, because if you’re innocent (the DNA isn’t yours, and you know it), the police are saying “we can and will create fake evidence to convict you.”
Plenty of innocent people would confess at that point.
Plenty of innocent people have. And many states permanently strip voting rights if you are convicted of (plead guilty to) a felony. So the folks most likely to have been adversely affected by this cannot take part in elections to fix the problem.
Check out public defender Twitter. It's a real eye-opener. Police officers still on the force but put on DA lists to never call because they've lied so often on the stand that even the judges know automatically they're full of it. (Almost never charged with perjury though.) Judges constantly handing out bail for minor offenses they know the defendant can't hope to pay even though they aren't a flight risk. DAs regularly withholding exculpatory evidence until just before a trial date in the hopes the (innocent) person agrees to a plea deal while they rot in holding for months.
Threatening to fake DNA evidence is just the tip of the iceberg.
There's a great netflix special about the drug lab in Massachussets. One lady was just straight up not testing samples at all, and marking them positive for the prosecution. Thousands were jailed this way. The chemist was only caught because her work was 4x as fast as her coworkers, so they investigated what was going on.
Now imagine how many smarter people than her just ran all the tests at normal speed, but faked the result. It'd be damn near impossible for them to get caught. I'd wager for every one caught, there are 10 that don't.
The distinction here is that this lie is so coercive that it's unethical to allow any confession or evidence following it.
What would you do if you don't have money for a lawyer, and the police say that your unassailable DNA evidence was found on a now-dead acquaintance of yours, and your options are confess to the murder and get 10 years with opportunity for parole, or fight and get life?
Even if you knew that the police can lie, know you are innocent but can't prove it, and you believe that the DNA test is real or the police are willing to fake it, you might confess b/c that's the best option.
It's not allowed in the Netherlands and Belgium. I thought it also wasn't allowed in the other european countries but I'm not a 100% sure about that.
If the police are allowed to lie about evidence then this undermines the suspects chances for a fair trial (false confession). If the defense can show at a trial that the police lied during the interrogation, this would impact the chance for a conviction. At least this is how it works in the EU. In the US, I have the impression the judges don't take this into account.
Plenty of innocent people would confess at that point.