Maryland teen was plotting mass school shooting, police say

— -- A Maryland high school student is expected to face charges after a journal with a detailed plan for a mass shooting at her school was found in her home, in addition to a shotgun and bomb-making materials, authorities said.

On March 23, the father of the suspect, Nichole Cevario, 18, told officials at Catoctin High School in Thurmont, Maryland, about a "potential threat of violence towards the school," the Frederick County Sheriff’s Office said, and his daughter "was immediately removed from the classroom and turned over to investigators."

Authorities searched Cevario's home where they found a shotgun with ammunition and "bomb-making materials to include pipes with end caps, shrapnel, fireworks, magnesium tape, and fuse material," the sheriff’s office said today.

Authorities also say they found a journal that "clearly planned out a mass shooting," Frederick County Sheriff Charles Jenkins said at a news conference this afternoon. The journal, which listed the suspect's school and a date in April, had a timeline and her expectations for each stage, the sheriff's office said.

The diary's first entry was Dec. 16, 2016, Jenkins said. Officials say the journal showed Cevario had been planning "for some time and had been compiling intelligence on behavior activities of the school, noting emergency procedures associated with drills conducted by school staff and obtaining intelligence on the School Resource Deputy," the sheriff’s office said.

"It shocks the conscience to see that someone of that age could be thinking like this,” Jenkins said.

There was never a weapon or explosive device on school property, authorities said, and the materials were never combined into an explosive device.

Jenkins said all the items Cevario bought were legal. Authorities said no one else was involved or knew of the alleged plot.

According to the diary, Cevario planned to die from the attack, officials said.

When Cevario was removed from the school on March 23 it appeared that she posed a threat to herself and she was taken to the hospital, where she remains today, the sheriff's office said. The sheriff's office said she was struggling with mental health issues.

Investigators secured an arrest warrant for possession of explosive material with intent to create a destructive device and possession of incendiary material with the intent to create a destructive device, the sheriff's office said. The arrest warrant will be served when she's released from the hospital, the sheriff's office said.

The sheriff’s office expressed its appreciation for Cevario's father who reported the potential threat and said he has been cooperative with the investigation. The sheriff's office did not know if Cevario had retained a lawyer.

In a video today on the school district's YouTube page, Dr. Terry Alban, superintendent of Frederick County Public Schools, thanked the "courageous" parents for stepping forward.

"Whenever you hear or see anything that raises concern, you need to trust us and come to us so that we can do the right thing and handle it just like we did in this case," Alban said. "Those relationships, that trust, that's what enables the policies and the procedures that we have put in place to keep our school safe work. And they did."

The school district did not immediately respond to a call for comment.

ABC News' Geneva Sands contributed to this report.