Courts have ruled that DNA collection does not fall under Miranda. That being said, a person can refuse.
I have never seen a case where a defense attorney successfully used thé increased scrutiny to persuade either judge or jury.
DNA was eventually obtained without a warrant.
Please don't put words in my mouth. I'm speaking from my own years of professional experience and that mantra had nothing to do with my statements.
I do know for a fact that if a bunch of people are asked to volunteer DNA samples, all of them being contacted because of a particular scenario that is leading an investigation, and ONE of them says Nope to the DNA that it is not at all difficult to obtain it - even without probable cause.
Courts have ruled, for example, that no probable cause is needed to grab a piece of trash left behind by any person. And "probable cause" covers many such situations. In this case, of course, LE is trying to rule people out not in, by asking for samples. Would a judge later agree that LE had probable cause to grab a straw out of a JitB trash bin, and the DNA on the straw leads them to the killer (as evidenced by many others things - not just the DNA)?
I think the judge would so rule (and likely would not hear about it otherwise - no one would, outside LE). If the DNA exonerates the person, it just goes in a file.
Naturally, LE doesn't do this unless they have suspicions about a particular person.