Paris investigators on Friday detained for questioning one of President Emmanuel Macron's top security aides who was caught on camera beating a protester in May, a turn of events that is evolving into the biggest political crisis to hit the president since he took office last year.

The presidential É​lysée Palace is taking steps to fire Alexandre Benalla, who was identified earlier this week by the newspaper Le Monde for beating a young protester during May Day protests while wearing a police helmet. A second man is also facing potential charges for involvement in the incident.

Macron, who has promised an exemplary presidency, has yet to respond.

The storm has prompted an impassioned debate in the French parliament about why it took 2½ months to inform judicial officials and why Benalla stayed in his post. Questions over whether there was an official coverup have also been raised, and whether Élysée employees have a measure of impunity not granted to others.

A parliamentary investigative committee is in place and began its work Friday.

"It's an illusion to think you can put a cover on things when you live in a democratic country," lawmaker and far-left leader Jean-Luc Mélenchon said to reporters. "In the end, everything is known."

France has been gripped by the video of the May 1 event in Paris showing Benalla, in a helmet with police markings and surrounded by riot police, brutally dragging away a woman from a demonstration and then beating a young man on the ground. The man is heard begging him to stop. Another man in civilian clothing had pulled the young man to the ground.

Police, who had yanked the man from the crowd before Benalla took over, didn't intervene. Benalla then left the scene. The second man was apparently a gendarme in the reserves who Le Monde said had worked with Benalla in the past.

Authorities moved into damage control soon after Le Monde identified Benalla in the video, which had previously been posted on the Internet, in its report Wednesday night.

The presidential palace notified judicial officials on Thursday of the violent scene and awkwardly explained that the Élysée had in May suspended Benalla for two weeks and gave him a desk job. The spokesman also said Benalla had been authorized to follow police operations on his day off on May Day "as an observer."

A judicial official said Friday that Benalla is being questioned on an array of counts. Among them is violence committed in a group by a person with a public service mission and misusing police insignia. The official spoke on condition of anonymity because of the ongoing investigation, which was launched Thursday. The second man, a gendarme in the reserves, who had worked with Benalla in the past, was detained hours later Friday.

By Friday, the president's office began proceedings to fire Benalla, based on unauthorized possession of an official video surveillance film that he obtained to help prove his innocence, an Élysée Palace official said.

Linked to that, the interior minister announced on Friday the suspension of three ranking police officers for allegedly giving the images to the security chief. Le Monde said the official images showed the violent scene from May.

Despite his official change to a desk job, Benalla was seen this month on the ground with police at several high-profile events, including the return home Monday of France's soccer World Cup-winning team, an event attended by hundreds of thousands.