The man who authorities said infamously killed two Virginia television journalists Wednesday was tracked down by police via license plate reader technology, according to law enforcement.

A Virginia state trooper told a news conference Wednesday that she hit Vester Lee Flanagan's plate number on her first try along Interstate 66 around 11:20am ET. "As soon as it was entered, it came up with a positive hit that that vehicle just passed me less than three minutes earlier," she said. "I let my dispatch know that the vehicle has passed me and I attempted to catch up with the vehicle, which was travelling eastbound on 66."

Moments later, police tried to stop the Chevrolet the man was driving. The vehicle drove off the road and crashed, and Flanagan, who also went by Bryce Williams, was discovered to have shot himself. He later died of his self-inflicted injuries.

"License plate readers are a great tool," said Sgt. Rick Garletts of the Virginia State Police. "It helped in that case to identify that vehicle."

WDBJ-TV journalists Alison Parker and Adam Ward were gunned down Wednesday on live TV.

LPR data can also be used as a surveillance tool against the law-abiding public, as Ars has repeatedly reported. In response to a public records request, we obtained the entire LPR dataset of the Oakland Police Department, including more than 4.6 million reads of over 1.1 million unique plates between December 23, 2010 and May 31, 2014. The dataset is likely one of the largest ever publicly released in the United States—perhaps in the world.

After analyzing this data with a custom-built visualization tool, Ars was able to definitively demonstrate the data's revelatory potential. Anyone in possession of enough data can often—but not always—make educated guesses about a target’s home or workplace, particularly when someone's movements are consistent (as with a regular commute).

The readers are usually mounted on roadside structures or on police patrol vehicles.