Tricking suspect into handing over DNA

The Washington Supreme court has ruled, in a divided opinion, that police acted lawfully in mailing a murder suspect an invitation to take part in a class action lawsuit to recover over-paid parking fines, and then analysing the seal on the letter he returned (which he had presumably licked) for his DNA. (For those interested in US constitutional law, the 4th amendment analysis starts on page 20 of the opinion).

I was interested in the dissents too, penned by justices Fairhurst and Chambers. Chambers for example says:

"Creative and inventive police work should be encouraged. But the police must work within the rule of law. I can say it no better than Justice Thurgood Marshall:

Good police work is something far different from catching the criminal at any price. It is equally important that the police as guardians of the law fulfil their responsibility to obey its commands scrupulously. For "in the end life and liberty can be as much endangered from illegal methods used to convict those thought to be criminals as from actual criminals themselves.""

Fairhurst is even more critical:

"The majority err's in thinking John Nicholas Athan's privacy interest is merely in his identity. It is not. Athan's privacy interests are in his bodily integrity and his genetic information. By mischaracterizing the privacy interest as one of identity, the court misapplies this court's established analysis... to the facts of this case.

The majority's applcation... is breathtaking in its sweep and impossible to reconciles other rulings of this court. Under the majority's holding the govenrment could analyze the DNA in anyone's saliva, however obtained, as long as it was not directly from the person's mouth, and use the information to construct a DNA database that incudes both felons and non felons. Because DNA holds the most intimate details about a person, I cannot agree with either the majority's holding or reasoning."

Dr Reid... meet Justices Chambers and Fairhurst. I guess, in defence of the majority, they did go through a process of reasoning which was neither superficial nor entirely politically self serving. Kudos to the detectives on catching a child killer but given the other evidence in the case wouldn't they have had enough to get a DNA sample through the conventional legal process? Do the ends justify the means if it leads to the rightful conviction of a child murderer? Can it ever be a rightful conviction if due process is not observed?