They are charged with....murder, robbery, rape...etc. Some cases are better than others. Sometimes they are caught red handed. They have confessed. There are multiple witnesses.
This isn't really about innocence or guilt though this is about unreasonable search. The person is already in custody. It takes 30 seconds to run a swab under their lip. Their identity is confirmed as to whom they are. If there is a hit on their DNA another case might be solved, or, an innocent person might even go free! Tell me what is so unreasonable about that swab?
I agree that police shouldn't over extend our authority but this isn't it. This is using the tools we have to do our job. It is not abusing citizens. It is not a fishing expedition as you or someone else proclaimed in an earlier post. It's getting bad people off of the street. Not at any extra cost. We are not bustin into people's homes, we are not stopping people on the street. We are not looking into peoples cars. We are processing them while they are being arrested. Nothing unreasonable about that.
I hope Tom is right. I hope it's overturned. If not, I hope you explain to the next rape victim why their rapist can't be convicted because you want to protect the rights of the person who raped them.