What prompted a Saugus High School student to bring a gun to school on his 16th birthday and shoot five classmates – fatally wounding two of them — before turning the gun on himself Thursday remains a mystery to investigators.

“The big question is why,” Los Angeles County Sheriff Alex Villanueva said during a television interview early Friday morning. The shooter, Nathaniel Tennosuke Berhow, died in the hospital on Friday just after 3:30 p.m., after being treated for a self-inflicted gunshot wound to the head, authorities said. His mother was present at the time of his passing. Two of the five victims, a 15-year-old girl and a 14-year-old boy, died earlier and were identified by coroner’s officials on Friday as Gracie Anne Muehlberger and Dominic Blackwell. Authorities conducted over 40 interviews but were unable to establish a rationale for the shooting, said Capt. Kent Wegener of the Sheriff’s Homicide Bureau at a press conference at noon Friday. Berhow wasn’t a loner, Villanueva said. “He wasn’t socially awkward. Was involved in student activities. A student athlete … this is kind of out of the blue,” he said.

Authorities did not find a manifesto, diary or suicide note that would identify a motive, Wegener said.

The FBI and the Bureau of Alcohol, Tobacco, Firearms and Explosives have joined the Sheriff’s Department in looking for clues. The school, located at 21900 Centurion Way in Santa Clarita, was treated as a crime scene, where evidence was collected and documented and a 3D scan was conducted, before being cleaned and returned to the school district Friday, Wenger said. Investigators have searched Berhow’s home in Santa Clarita and are digging through his social media accounts. “Still we don’t have the answers we’re looking for,” Villanueva said. An Instagram account that initially appeared to be tied to Berhow did not, in fact, belong to him, a company spokesperson confirmed to KTLA. The account had a bio that read, “Saugus have fun at school tomorrow,” prior to Thursday’s shooting.

The account was disabled for violating Instagram policies, spokesperson Stephanie Otway said. It was not immediately clear who owns the account. Surveillance video from the school has helped investigators piece together the tragic events that occurred Thursday morning. Around 7:30 a.m., the video shows Berhow walking into the school’s quad area. “He was just standing there, really not engaged with anyone,” Villanueva said. At one point, Berhow takes off his backpack, reaches in and retrieves .45-caliber semi-automatic pistol. The gun actually jammed after firing the first round but he cleared the malfunction and then fired again at the remaining four victims, Villanueva said. “He used literally six rounds that he fired and he saved the last round for himself,” Villanueva said. It was a planned attack, he added.

The entire incident lasted only 16 seconds, according to investigators. The gunman never chased any of his victims and appeared to just shoot whoever was there at the time, Villanueva said. Three off-duty members of law enforcement were the first to respond to the shooting and render aid to the wounded students. Six students, including the gunman, were transported to local hospitals. Two, Muehlberger and Blackwell, were later pronounced dead. No further information was given due to a security hold on the case, the official stated. Two girls, ages 14 and 15, were expected to be discharged from the Providence Holy Cross Medical Center the next day or so, their doctors said Friday. The 14-year-old was shot in the left shoulder and lower right abdomen. A bullet hit the 15-year-old below the belly button and traveled to her hip, her doctor said. The other victim, a 14-year-old boy, was released Thursday. Berhow was said to be in grave condition at Henry Mayo Hospital following the shooting before he was pronounced dead Friday afternoon.

Villanueva said Berhow was living with his mother and there had been no service history of calls to the residence. Berhow’s father had passed away in 2017 from natural causes, he said. Investigators said it was still unclear how Berhow was in possession of the gun. This was the 142nd school shooting involving a minor with access to a firearm since 2010, Villanueva said. Several vigils and prayer services were held in honor of the victims Thursday night. A growing memorial could also be seen Friday morning at nearby Central Park, where many of the students ran to safety as the shots rang out.