Ten people have been killed and 10 others injured after a student opened fire at a Texas high school, the state governor said.
The attacker, who was arrested and charged with murder, was identified as Dimitrios Pagourtzis, a 17-year-old pupil at Santa Fe High School.
He allegedly used a shotgun and a revolver taken from his father, who legally owned the weapons.
Most of the dead are students, police said.
Texas Governor Greg Abbott said "various kinds of explosive devices" had been found at the school, 40 miles (65km) south of Houston, and off-campus. They included "a CO2 device" and "a Molotov cocktail", he said.
Mr Abbott said police found information on the suspect's diary, computer, and mobile phone suggesting that he planned the attack and intended to kill himself afterwards.
The governor said the teenager "gave himself up" because "he didn't have the courage to commit the suicide".
Santa Fe Police Chief Jeff Powell advised residents to be aware of any suspicious objects they find. "Do not touch any items that look out of place," he said.
Santa Fe school police officer John Barnes has been named among the injured. He was in a critical condition and undergoing surgery, local media reported.
Also on Friday, one woman died and another was injured in a shooting outside a high school graduation ceremony in in Atlanta.
So far this year, more than 5,000 people have died in shooting incidents in the United States, according to monitoring group the Gun Violence Archive.