I know it's not exactly the point, but the answer is you always have a lawyer if you're being questioned by the police, especially if you're not the one who called them. This is in no way specific to any DNA related situation. If any law enforcement shows up and has questions for you, you say nothing until you have a lawyer with you.
Doesn't matter. If they're talking to you say you need your lawyer present -- that will end the interrogation, and you might never need a lawyer. But if you don't say that you might end up convicted.
I'm not saying it's fair or right. As with most things in life, the cost/benefit makes it likely you'll have to take some risks, but people need to understand that literally any interaction with any law enforcement without a lawyer present is a risk of things going horrifically badly. This is especially true if they show up and you do not know why. That is a massive set of alarm bells that should be going off.
If you can’t afford a lawyer just say nothing. Nothing you say will help you; anything you say can be used against you. If you say nothing you force them to use other evidence which they likely don’t have.
Police (in the U.S. anyways) are allowed to use ruses almost without limits, so you might not even know you're being interrogated, and your answers can be used against you (and only against you -- never to exculpate you!) in a court of law.
IMO the hearsay rule is way too biased in favor of the government.
Worse! Say you know it's police asking you questions, and the questions are all very harmless, so you answer them, but then you start to get an inkling that you are a suspect, that they like you for some crime, so now you shut up and/or lawyer up, but guess what: your disposition's change from cooperative to non-cooperative can and will be used against you in a court of law!! What, you say? Yes, the SCOTUS in the 2010s (see Salinas vs. Texas, from.. 2014 IIRC) greatly reduced the 5th Amendment's protections in this way. If you're talking then clam up, the fact that you clammed up -and at what particular question- can be used against you. And if you never said a word to them, that too can be used against you! The only thing that works is to tell them very early on that you will only talk to them with your lawyer present [and since you don't have a lawyer yet you might never talk to them] then follow through.
If the police are talking to you it's either a) they think your testimony can convict someone else, and/or b) they like you for some crime and want to give you ample opportunity to convict yourself of it even if you didn't commit it (they may not know that, but they may like you so much for it that their bias is too strong to see that you're innocent) and even if you have no idea what the heck they're talking about (because they don't even have to tell you).
See all of professor James Duane's videos on this topic, starting with Don't Talk to Police (this one is pre-Salinas), and then the later post-Salinas reprise(s) of it.
I mean, assume any time you're talking with the police, you're being interrogated. If you called them yourself for something, then you've decided to take that risk, but that's also a situation where you're less likely to be in trouble yourself, though there's still a risk.
Lawyers are expensive. Most people can't afford one for even one encounter with the police, let alone multiple.