The facts briefly are that Alonzo King arrested in 2009 for assault was subject to DNA testing that linked him to a 2003 rape. The American Civil Liberties Union argues that this is a violation of privacy and that at the minimum a warrant should be required.
I don't see how a swab test taken as a result of an arrest which comes out to be a DNA match with another unsolved outstanding claim would be considered a violation of privacy or due process. In fact it provides that perfect balance. What my take is that taking a DNA test from a person arrested for an assault charge is neither an unreasonable search nor seizure. If x y z breaks the law and is then put on a database and matched with another crime, it is an exercise in state efficiency and not unreasonable search or seizure.
It would be unreasonable search or seizure if people were randomly tested and recorded. A person who breaks the law does so knowing that he or she would now be on a database and that database may be cross referenced and matched.
I expect the US Supreme Court to uphold the Maryland Law.