Police in Florida arrest a 19-year-old after they say they found written shooting spree threats during a routine traffic stop

Authorities in South Florida say they arrested a 19-year-old this week after they say they found written threats for a shooting spree and other attacks in his vehicle during a routine traffic stop.

A Jupiter, Florida, police officer pulled over Henry Horton IV on September 18 for a headlight that was out on the white pickup truck he was driving, according to a probable cause affidavit from the Palm Beach County Sheriff's Office.

During a search of Horton's vehicle, the officer found multiple handwritten notes with a plan to purchase firearms and "kill everyone at OHS (Okeechobee High School) with my guns," the probable cause affidavit says.

Horton graduated from the high school, located in Okeechobee County, in May 2022.

Horton told the officer he had previous mental health issues and had "been having multiple thoughts about mass homicide and want(ing) to execute them once he turned 22 years old," according to the affidavit.

He had plans to kill 15 people from the high school on January 2, 2026, his 22nd birthday, according to the affidavit.

Horton said while living in Virginia, he voluntarily admitted himself to a medical facility for a mental health evaluation due to having similar thoughts, the affidavit stated.

Authorities asked him where he was heading before getting stopped. Horton said he was traveling to Miami to look at a church, where he told investigators he planned to kill around 10 people following his planned 2026 attack at his former school, according to the affidavit.

Horton was transported to a hospital to receive a mental health evaluation under the Florida Mental Health Act, commonly known as the Baker Act, which allows people to be involuntarily detained and subject to an examination for up to 72 hours during a mental health crisis.

The Okeechobee County School District is working with the sheriff's office and state attorney's office on this case, superintendent Ken Kenworthy told CNN in a written statement.

"The district will pursue every recourse within its power to protect all school campuses and property where staff and students reside," Kenworthy said.

Horton told investigators he had also visited and studied Marjory Stoneman Douglas High School in Parkland, Florida, the affidavit says.

A mass shooter killed 17 people and injured 17 others at the Broward County school on Valentine's Day 2018.

On September 29, authorities say Horton admitted to investigators he wrote a manifesto and had written threats to kill his stepmother.

Investigators issued an arrest warrant for Horton, who was arrested on Thursday. Horton has been charged with intimidation with written threats to kill or harm another individual, according to jail records.

He remains booked in the Palm Beach County Jail on a $1 million bond.

Horton is scheduled to appear in court on November 6, according to court records. CNN has been unable to determine if Horton has legal representation at this time.

CNN has reached out to Okeechobee High School and to the public defender assigned to Horton.

CNN's Ashley R. Williams contributed to this report.