Ten people have been killed and ten others were injured in a Texas high school shooting.
Students said a gunman, identified by police as Dimitrios Pagourtzis, opened fire in a classroom at Santa Fe High School shortly before 8am local time.
The students then fled in panic after seeing classmates wounded and a fire alarm triggered a full evacuation.
The Galveston County Sheriff's Office identified the suspect and said he had been charged with capital murder in a post on its Facebook page.
More charges could follow for Pagourtzis, who was a student at the school.
Speaking to reporters before the teen was identified, Texas governor Greg Abbott said that the suspect had used a shotgun and a .38 revolver taken from his father in the fourth-deadliest mass shooting at a US public school.
A second possible person of interest has also been detained and is being questioned, according to Harris County Sheriff, Ed Gonzalez.
In a post on Twitter, Mr Gonzalez said that explosive devices were also found at the school, located about 48km southeast of Houston.
Police were searching two homes and a vehicle linked to Pagourtzis, where they have found multiple homemade explosive devices, Mr Abbott said.
The school has some 1,462 students, according to US federal education data.
Ten people dead following shooting at Texas high school | https://t.co/0DlRE5Vqy6 pic.twitter.com/sjKkJWCD6q
— RTÉ News (@rtenews) May 18, 2018
US President Donald Trump expressed his "heartbreak" at the "absolutely horrific" shooting.
"My administration is determined to do everything in our power to protect our students, secure our schools and to keep weapons out of the hands of those who pose a threat to themselves and to others," he said at the White House.
School shooting in Texas. Early reports not looking good. God bless all!
— Donald J. Trump (@realDonaldTrump) May 18, 2018
The latest shooting at a US school underscored a national debate over gun control and gun rights that has intensified after 17 students and staff were killed in a shooting at Marjory Stoneman Douglas High School in Parkland, Florida last February.
