PARIS — A deadly attack this week at the Strasbourg Christmas market in France by a suspect who was on a watch list as a possible security risk has drawn scrutiny once again to how the authorities handle suspects who have been flagged as potential threats.

The suspect, Chérif Chekatt, 29, was killed on Thursday night after a hunt by French security forces. Armed with a knife and a handgun, he killed four people, left another brain-dead and injured 11 others. The authorities described the Christmas market rampage on Tuesday as a terrorist attack.

Mr. Chekatt had a long police record, and he had also been flagged by the French security services for possible radicalization, putting him in a database of people who are suspected of religious extremism. He was also in a separate database for people tagged with a Fiche S, or S File.

What is an ‘S’ file?

The S File is a category in a much larger database of people who, for a variety of reasons, are of interest to the French authorities. (Other categories include “M,” for runaway minors, or “V,” for escaped prisoners.) The “S” stands for la Sûreté de l’État, or security of the state.