As of Tuesday afternoon, two 15-year-old students - one male and one female - had died and more than a dozen others were injured.
Authorities say the 16-year-old boy who opened fire inside the school has been charged as a juvenile with two counts of aggravated assault with a deadly weapon.
The shooter is now in police custody and will be charged with two counts of murder and several counts of attempted murder, according to Kentucky Governor Matt Bevin.
State police didn't provide any other immediate details about the shooter or the apprehension.
Marshall High had 1,300 students in the 2014-2015 school year, according to the National Center for Education Statistics.
Kentucky State Police Lt. Michael Webb said detectives are looking into the suspect's home life and background. I turned around and then I see this guy turn from his side. "I was like, 'If we don't do something, we are going to have another Heath High School or another Sandy Hook situation, it's just a matter of time.' And yesterday proved that to be the case". And then it registered. School officials said they depend on students to tell an adult if they see something out of the ordinary. I heard some hit the ground.
He added his hand was grazed by a bullet.
The names of the two people killed during a high school shooting in Marshall County, Kentucky were released Tuesday evening.
"We feel all the prayers and so appreciate the support", she said.
Bailey Holt, 15, was one of two students killed in the shooting.
A further 14 students are being treated for gunshot wounds, while five more sustained injuries including a fractured jaw while trying to escape.
"I have children in school as well and I'm not unimpacted by the events that take place in our world".
Backpacks, cellphones and clothes were strewn in the main area where the shooting occurred, he said. "It made it real, seeing the disarray". "It is unbelievable that this would happen in small, close-knit community like Marshall County".
Benton is a city of roughly 4,500 people.
Speaking on the floor of the U.S. Senate, McConnell says his staff in western Kentucky is at Marshall County High School and is in close contact with local officials.
In a tweet from a verified account, Gov. Matt Bevin said it happened at Marshall County High School in southwest Kentucky.
"There's no good answer for it", Bevin said.
"Everyone that was in the library, once they saw what was happening, we all started running towards the library office and once we got in there, we just shut the lights off, sat down, locked the doors", another student said.
Bailey died at the high school and Preston died at Vanderbilt University Medical Center in Nashville, CNN reported quoting State Police Commissioner Richard W. Sanders.
White House Press Secretary Sarah Sanders said the president has been briefed on the shooting. "Our thoughts and prayers are with the victims and the families there", she said.