French Le Monde newspaper said Wednesday that Benalla was identified in a May 1 video where he was captured tackling a young man to the ground and punching him repeatedly before fleeing.
"We filed a suit today in the afternoon to determine how it could happen, how a man turned out to be in the role of an observer, how he got an armband, a helmet, how he managed to go unpunished," Alexandre Langlois told the BFMTV broadcaster.
Earlier on Thursday, media reported that Paris prosecutors launched a preliminary investigation into the incident, treating the case as a potential act of violence committed by a person holding public office.
Benalla was suspended from duties for two weeks.