A court determined on Friday that 15-year-old Jesse Osborne will be tried as an adult on charges stemming from the deadly shooting at Townville Elementary School in 2016.

Osborne was arrested at the age of 14 after investigators said he opened fire on the elementary school playground, striking 6-year-old Jacob Hall. Jacob passed away three days after the shooting.

He is also charged with murder in the fatal shooting of his father, Jeffrey Osborne, just hours prior to his suspected attack on the school on Sep. 28, 2016.

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In a five-day hearing to determine how Osborne should be tried, state prosecutors called nearly 20 witnesses who testified on his past, mental health, internet activity and more.

A 46-page transcript was released of when investigators said Osborne confessed while detained after the shooting. The defense argued the confession should be inadmissible since Osborne was questioned without a parent or lawyer present. A judge, however, ruled the confession was voluntary and would be allowed.

READ MORE: Court releases 46-page transcript of Townville shooting suspect's confession

The confession transcript states that Osborne told authorities he was angry after being bullied. He also said after shooting his father and before driving to Townville Elementary, he kissed his pet rabbit and three dogs goodbye, the document states.

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FBI Special Agent Shandal Ewing testified that messages from an Instagram account created by Osborne detailed plans to attack the school days before the shooting.

Messages included plans to "most likely kill around 50 or 60" and to "then get in a shoot out with police then kill myself with my shotgun."

READ MORE: 'I want them to be stuck in a corner': FBI details messages sent by Townville shooting suspect

Prosecutors argued Osborne had a fascination with other mass shooters, including Dylann Roof, Eric Harris, Dylan Khlebold, and Omar Mateen. The state presented evidence recovered from Osborne's phone depicting images of these shooters along with memes making light of mass shootings.

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An Anderson County digital forensics investigator testified that Osborne had searched the internet for graphic websites and video depicting torture. Following his arrest, a Greenville County Schools teacher who instructs at the juvenile detention center said Osborne listened to a rap song more than 50 times on his computer containing graphic lyrics including a threat to shoot up a town.

SLIDESHOW: Evidence from Townville shooting suspect's phone

On Thursday, psychologist Dr. James Ballenger testified that Osborne showed no signs of a psychiatric disorder and appeared to be developmentally above average. Ballenger said Osborne is indifferent toward his victims, saying the suspect claimed he did Jacob "a favor" and that Osborne cared "more about his image of being the best shooter than how he is going to be punished."

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READ MORE: Psychiatrist in court: Townville school shooting suspect displayed no signs of psychiatric disorder, should be tried as adult

The state called forward witnesses including a psychologist who testified that Osborne told them he had been physically and verbally abused by his father and by bullies. Dr. Ernest Martin said Osborne showed signs of mild depression with psychotic features and post-traumatic stress disorder. A minister also testified that Osborne had been kind and thoughtful in their interactions and said Osborne had asked for prayers to get the help he needed.

The testimony, however, did not convince a judge that Osborne should be tried under juvenile status.

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Due to his age, Osborne is not eligible for the death penalty if convicted, but he could face up to life in prison. He is charged with two counts of murder and three counts of attempted murder.

Solicitor David Wagner said he was pleased with the outcome of the hearing.

"The people of Townville have shown this week what it means to be 'Townville strong' as they listened to the testimony and supported each other," Wagner said. "Our hearts continue to be with them as we move forward to the next phase of this long process."

FULL COVERAGE: Townville school shooting headlines

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