It took three minutes for James Palmer to make it from the entrance of an Arkansas courthouse to the chambers of the judge he intended to kill. Dressed in a long coat that hid two handguns and a rifle, Palmer went undetected on Sept. 13, 2011 — until he started firing. A secretary was injured in the leg, but the judge was at home that day. Palmer fired more than 70 rounds before dying in a firefight with officers.

St. Louis judges considered such a scenario in approving a pilot program for security at the Carnahan Courthouse downtown that brings a new twist to law enforcement’s emerging use of facial recognition technology.

Unlike programs that have alarmed civil libertarians for snapping pictures of people to run through giant databases of mugshots and arrest records, what’s being done here is much more targeted. If a judge or prosecutor knows of a particular threat — someone such as Palmer, for example, who was angry at the judge over divorce and custody issues — that individual’s photograph is put into a computer system. It sends an alert if that person is spotted by cameras at the courthouse entrances.

A group of current and retired St. Louis police officers developed the technology over eight years and recently formed a company, Blue Line Security Solutions, to market it. […]