A 15-year-old sophomore has been apprehended for sparking a deadly high school shooting in Michigan, which killed at least three students, aged 14, 16, and 17, and injured eight others, including a teacher, on Tuesday night. 

According to authorities, the lone teen suspect fired 15 to 20 shots with a semi-automatic handgun, but his motives for the attack in Oxford, a town of 22,000 and about 40 miles from Detroit, remain unknown.

In a news conference outside Oxford High School on Tuesday, Oakland County Undersheriff Mike McCabe said 911 phones started to ring hot at 12:51 p.m., logging at least 100 calls within minutes, according to BBC

In terrifying 52-second footage that went viral on social media, a group of students can be seen hunkered down after barricading themselves in classrooms. They are also shown hiding behind furniture while the unidentified gunman allegedly impersonated a sheriff in the hallway.

“Sheriff’s office. It’s safe to come out,” a young male voice can be heard from behind the door of the Oxford High School classroom during the shooting as per the New York Post.

The frightened students would refuse to come out, skeptical of the supposed authority figure. One girl would also whisper, “We don’t know who that is.”

When another student standing by the door sternly said, “We’re not taking that risk right now," to the man behind the door, the male voice reportedly used casual language and replied, “OK, well, just open the door, and look at my eyes, bro.”

“He said, ‘Bro.’ Red flag!” a male student says before his classmates started jumping out of the first-story windows. They would run through the snow to the main entrance of the school, where a uniformed officer assured them they were already safe.

Police arrested the alleged gunman five minutes after 911 was inundated with calls from the school.

“Deputies confronted him, he had the weapon on him, they took him into custody,” Oakland County Undersheriff Mike McCabe said, adding that the suspect’s motives were unknown.

Earlier this month, police responded to calls of a vandalism incident at the school, which involved graffiti and a severed deer head. Police said investigations found the two vandals were not linked and were not deemed as “warning signs” of the shooter’s plan, the Daily Beast reported.

police line Authorities have confirmed that their operation took a tragic turn after the twin of the suspect they were pursuing reportedly “brandished a firearm at responding law enforcement,” prompting local cops to return fire, which eventually killed Deaughn Willis on Saturday. This is a representational image. Mark Winema/Getty Images