MemeMachineGo!

Swabbing without a warrant:

Recently, the police asked Shannon F. Kohler if they could swab the inside of his mouth to analyze his DNA. It was a request they made of 800 men in southern Louisiana as they searched for the serial killer who has slain four young women, leaving behind genetic material in each case.

It was his choice, Mr. Kohler said the officers told him, but if he refused, they would get a court order and that would get in the newspapers and then everyone would know he was not cooperating. The approach was heavy-handed and foolish, he said, especially since he has feet much bigger than the prints left by the killer and had phone bills that show he was at home when the murders took place.

[...] The idea for a DNA dragnet — sampling people who are not suspects but merely live or work near a crime scene — emerged in Britain. In 1987, the police tested 4,000 men in Leicestershire before the rapist and killer of two girls was caught after he got another man to take the DNA test for him.

Just for giggles, here's the 4th Amendment:

The right of the people to be secure in their persons, [emphasis added] houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, and no Warrants shall issue, but upon probable cause, supported by Oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized.

In "Gattaca", one of the better sf films ever (which isn't to say that it was a great film, but it's one of very few films that's truly science fictional as opposed to being action/adventure or horror with sf props), the cops of a near-future world with fast, cheap DNA testing are portrayed as having become one-trick ponies with DNA dragnets as their approach to everything. Props to Andrew Niccol (who also wrote "The Truman Show").