One of the New York City teens wanted in connection with Saturday's brutal assault of an FDNY firefighter was arrested early Thursday morning, the NYPD officials confirmed to Fox News.

Damir Johnson, 17, was charged with one count of second-degree assault after police identified him as a member of the group that assaulted the firefighter, leaving that man with several broken teeth and a concussion. Cops released an image on Wednesday of the six suspects, but they didn't immediately identify which of the teens in the picture was Johnson.

Saturday's incident began when the unidentified 38-year-old firefighter, traveling on East 86th St. in Manhattan around 9:25 a.m., said he noticed the three males and three females -- all thought to be between 15 and 17 years old -- “harassing” an elderly couple.

OFF-DUTY FDNY FIREFIGHTER ATTACKED BY TEENS AFTER DEFENDING ELDERLY COUPLE, COPS SAY

When he tried to intervene, the off-duty firefighter was hit "with a closed fist" by one member of the group, police said. The sucker punch knocked the firefighter to the ground -- at which point at least one member of the group continued assaulting the man. It's not clear what role investigators believe Johnson may have played in the incident.

Police released surveillance footage of the six teens Wednesday and in less than a day had identified Johnson and taken him into custody.

Cops arrested Johnson after a tip came through the Crime Stoppers hotline which led investigators to question the teen's family, the New York Daily News reported. Johnson was subsequently arrested at his home in Harlem.

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The unidentified firefighter suffered a concussion and several broken teeth but has since been released from the hospital.