The FBI confirmed Thursday that it has begun a formal investigation into the case of a high-school student punched in the face repeatedly by a plainclothes sheriff’s deputy in Jefferson Parish.

The inquiry, which remains in its earliest phases, appears to be focused on whether the deputy, Detective Nicholas Breaux, used excessive force during a violent arrest this month in which he delivered four right hooks to the face of 17-year-old Brady Becker, a student at St. Charles Catholic High School in LaPlace.

“The FBI has an open investigation and is investigating this matter with the Jefferson Parish Sheriff’s Office,” said Craig Betbeze, a spokesman for the FBI’s New Orleans Field Office.

Becker’s attorney, David Belfield, said he was contacted Wednesday by Special Agent Steven Zeringue, an investigator assigned to the FBI’s civil rights squad, who informed him of the federal interest in the case.

“I’m told that the Department of Justice is pushing an investigation into this incident with Brady,” Belfield said. “They are wanting to interview Brady and all of the witnesses we have who were out there.”

The Feb. 13 arrest gained widespread attention after a 37-second cellphone video, recorded by one of Becker’s friends, showed Breaux trying to subdue the youth in the parking garage of the Lakeside Shopping Center.

The video, which has been viewed more than 319,000 times on YouTube, did not show the entire incident. But the footage did feature clear footage of Breaux striking Becker in the face, raising questions about whether the deputy, a mixed martial arts fighter, used excessive force.

Breaux, a seven-year veteran of the Sheriff’s Office, accused Becker, 17, of instigating the violence by pushing him and throwing the first punch, which Becker has denied. A five-page Sheriff’s Office report released last week said Becker had been among a loud group of people who started chanting “F*** the police” after officers tried to disperse a crowd that had gathered to watch the Krewe of Centurions parade.

The student, who allegedly told the authorities he had consumed a half-bottle of whiskey that night, was booked on several counts following the incident, including battery of a police officer and inciting a riot.

Belfield, who has drafted a federal civil rights lawsuit to file on Becker’s behalf, said Zeringue seemed “anxious to get this investigation concluded.”

The Jefferson Parish Sheriff’s Office also has begun an internal investigation into Becker’s arrest, though officials have said they don’t suspect wrongdoing on the part of Breaux.

Many observers have expressed concern about the tactics Breaux used in detaining Becker. But Greg Meyer, a nationally recognized expert on use of force by police, noted that Becker can be seen in the video “using both hands to reach up and grab the officer at the neck and shoulder area.” Meyer, a retired Los Angeles Police Department captain, said a decisive issue will be “figuring out whether (Breaux) was reacting to the subject’s actions, or the subject was reacting to the officer’s actions.”

David S. Weinstein, a former federal prosecutor who is now in private practice in Miami, said the FBI would examine the cellphone video but also Breaux’s history at the Sheriff’s Office, including whether he’s had any prior incidents involving the alleged use of excessive force.

The Sheriff’s Office this week rejected a public records request seeking Breaux’s disciplinary file, saying that information is shielded by a 2004 ruling by the state 5th Circuit Court of Appeal that found an assistant Jefferson Parish fire chief’s personnel records should be protected from “unnecessary public scrutiny.”

The FBI, Weinstein said, will use an “objective reasonableness test,” a standard that weighs the level of force Breaux used against the severity of Becker’s alleged crimes, the immediacy of the threat Becker posed and whether or not he sought to evade or resist arrest.

“It’s not that clear of a line,” Weinstein said, adding that the investigation could take several months to complete. “You can’t really insert yourself into the situation. It’s what the objective police officer would have done at the time.”

Weinstein said his initial reaction to the video had been that Breaux used a shocking and unreasonable degree of force. But he developed a different view after watching it several times.

“It looks to me that the officer simply reacted to what he thought was this kid choking him,” he said. “Perhaps in his mind, punching the kid in the head that many times was less excessive than pulling out a gun.”

Becker, who has called for Breaux to be fired, has since returned to classes at St. Charles Catholic High School.

Becker received two black eyes during his encounter with Breaux, and Belfield said the youth’s family had new concerns about long-term damage he may have sustained to his left eye, which began bleeding Wednesday. “His eye is in real bad shape,” Belfield said. “The doctors indicated there was some possible retina and muscle damage.”

Betbeze, the FBI spokesman, asked that anyone with information about the case contact the FBI’s office at (504) 816-3000.

Follow Jim Mustian on Twitter, @JimMustian.