The gun scare began when three students were in a bathroom and one of them heard what sounded like the racking of a gun, police said. They called 911 who dispatched it as an active shooter call, prompting the massive police response to the school.
After doing a thorough search of the school "floor by floor, room by room," authorities said no shots were fire and no gun was found.
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"I was just sitting in my second hour and I was writing an essay, and they said 'lockdown,'" said Phillip Ledet, student. "Everyone thought it was a drill."
"We heard the principal screaming 'Lockdown, lockdown!' on the radio," said student Brian Lagunas.
Teachers didn't have an answer when students asked if the situation was real. That's how they knew it was.
"At that point we were like, 'Well if you don't know then it has to be real,'" said Icyss Meredith, student.
But the school, teachers and students alike, were prepared. They texted their parents to let them know they were safe and sheltering. They took cover under desks, and teacher barricaded the doors. And eventually, they all were safely evacuated.
The school's resource officer was able to determine there was no threat "almost immediately" and was able to locate the two students believed to be involved.
Police said the massive response was due to the student's account of what he thought he heard, leading dispatchers to believe there was a possible active shooting threat.
Parents waited outside, frustrated with the lack of information except for text messages from their kids inside.
St. John police said there was an initial call about 9:30 a.m. of an active shooter at Lake Central High School, but once officers responded, it appeared that no one was hurt.
Superintendent Dr. Larry Veracco said two suspects are in custody and no shots were fired, according to a tweet posted on the school's student-run news outlet's account.
Parents rushed to the school, relieved as they greeted their children after the unexpected situation.
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U.S. 41, or Wicker Avenue, was closed between 77th and 85th in St. John during the investigation.
Police agencies from East Chicago to Cedar Lake, as well as ATF and FBI, assisted to the response.