n. In a criminal investigation, requesting DNA samples from a large number of people in an area where the crime is thought to have occurred or where the suspect is thought to be living.
On Wednesday this week, police canvassed the west-end streets where Holly was last seen, asking men "over a certain age" and who met certain criteria for saliva swabs. …

Experts say such massive DNA sweeps can have a sobering social and legal price.

Besides eroding civil liberties and tearing neighbourhoods apart, a sweep — known as a "blooding" — can compromise the value of any DNA evidence it yields.
—Allison Dunfield & Kirk Makin, “Random DNA sampling questioned,” The Globe and Mail, May 23, 2003
This case marked the first time that a murder was solved by the new procedure, developed by Dr. Alec Jeffreys at Leicester University in 1984. It allows investigators to read a individual's genetic code in a drop of blood or saliva or semen, and use that code to track down the criminal.

That's just what the police in Leicestershire did: Stymied, they tried this new procedure and ended up "blooding", the English term for taking blood samples, more than 4,500 males to find the killer.
—Laurence Chollet, “The cop-turned-writer on the beat,” The Record, February 21, 1989
1989 (earliest)
The decision was made, and announced the day after New Year's 1987, that the murder inquiry was about to embark on a "revolutionary step" in the hunt for the killer of Lynda Mann and Dawn Ashworth. All unalibied male residents in the villages between the ages of seventeen and thirty-four year would be asked to submit blood and saliva samples voluntarily in order to "eliminate them" as suspects in the footpath murders…The cops quickly began to refer to their testing sessions as bloodings.
—Joseph Wambaugh, The Blooding, William Morrow and Company, February 01, 1989
The word blooding, in the sense of "the letting of blood," actually dates to 1597. In the criminological context, it originally meant, simply, "taking a large number of blood samples." The purpose was to analyze the blood to do genetic fingerprinting (1984) — comparing each person's DNA with DNA samples obtained from a crime scene. Nowadays, as the example citations make clear, blooding has the more general definition of obtaining DNA samples by any method, including saliva.
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