http://blog.wired.com/27bstroke6/2008/05/feds-to-collect.html

“The feds will soon be collecting about one million DNA samples a year under a new program that lets federal agents collect cheek swabs from citizens merely arrested for any federal crime or from any non-citizen detained by federal agents—including visitors to the country who have visas.”
“The intent is [to] build a massive database of DNA samples that police can use to catch rapists and murderers, but even the innocent should fear being in the database, due to the vagaries of how cold case DNA searches can easily pinpoint an innocent person.”
“… As you start testing DNA profiles against more and more people, the chances that you will match an innocent person to a DNA profile from a crime scene gets higher.”