Prior to stabbing a 13-year-old boy to death and injuring two others at a Monday sleepover, a Florida teenager watched jihadist videos and read the Koran “to give him courage” to perpetrate the violence.

Corey Johnson, 17, who was previously investigated for “alleged violent tendencies,” was charged with first-degree murder and attempted first-degree murder after confessing to authorities that he committed the assault. The crimes occurred during a 13th birthday sleepover at a home in the BallenIsles Country Club area of Palm Beach Gardens.

Jupiter Police, Palm Beach County School District police and the FBI previously received “intelligence gathering” on Johnson, initiating an investigation into his “alleged violent tendencies,” the Palm Beach Post reported. The outcome of those investigations are unknown.

Johnson confessed to police that, during the sleepover at Kyle Bancroft’s home, he woke up at 4 a.m. Monday and had the urge to murder Kyle’s mother, Elaine Simon; Kyle’s brother, 13-year-old Dane Bancroft; and Dane’s friend, 13-year-old Jovanni Sierra, all of whom were asleep at the time. Johnson had brought a knife to the sleepover, which he used to stab Sierra multiple times before slitting his throat.

Apparently having heard a commotion, Simon began walking upstairs around 6 a.m. and Johnson allegedly lunged at her, stabbing her at least a dozen times before she fell down the stairs. Dane attempted to help his mother and was stabbed 32 times.

Simon was eventually able to run to a neighbor’s home and beg them to call 911.

“She rang my bell, she’s bleeding,” the neighbor said. “Corey Johnson is out there with a knife. He’s a murderer. That’s all I know. ”

Sierra was pronounced dead at the scene. Simon and Dane were transported to the hospital, where Simon was listed in good condition as of Tuesday. No information was released on Dane’s condition because he is a minor.

“He’s a hero,” Dane’s father said in a phone interview with the Post. “He saved his mom.”

Kyle Bancroft and Johnson remained unharmed in the incident.

After briefly barricading himself in a room, Johnson was taken into custody about 8 a.m.

“In his statement, Johnson advised he stabbed the victims because of his Muslim faith,” the affidavit stated, and also indicated that he had read the Koran before going to the sleepover “to give him courage to carry out his intentions.”

The night before the attacks, Johnson and Kyle Bancroft allegedly watched violent jihadist videos.

Johnson told police that he was upset with Sierra because he referred to celebrities as “gods,” which went against his Muslim faith. According to Johnson, Dane made fun of his faith.

Johnson recently withdrew from William T. Dwyer High School in Palm Beach Gardens.