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One teenager was killed and a second injured after a rocket exploded, possibly while one of the victims was holding it, according to fire officials in Thousand Oaks.

Emergency crews were called to Madrona Elementary School located at 612 Camino Manzanas around 7:40 p.m., Capt. Mike Lindbery with the Ventura County Fire Department stated.

The two injured teenagers were taken to the hospital, Lindbery stated.

The victims were described only as an 18-year-old male and a 17-year-old male. Both were students at Thousand Oaks High School.

It was later confirmed that the 18-year-old, who was most seriously injured in the explosion, died at the hospital, according to Detective Tim Lohman with the Ventura County Sheriff’s Department.

The device was initially described as a hobby rocket or model rocket, but investigators later clarified it was unclear what type of explosive the teenagers were using or whether it was part of a school project.

Update: Explosion That Killed Teen, Injured Boy Was Not Caused by Store-Bought Rocket, Official Says

Their names were not released.

Madrona Elementary School would remain closed Tuesday, Lohman said.