An Alaska teenager allegedly killed her supposed best friend after a man she met online promised to pay her $9 million if she sent him photos and videos of the killing.

Cynthia 'CeeCee' Hoffman, 19, was found dead with a gunshot wound to the back of her head and bound with duct tape near a hiking trail in rural Anchorage on June 2.

Her best friend Denali Brehmer, 18, and four other teens were arrested and charged over her murder earlier this month.

Police would not reveal a motive at the time but disturbing new details have emerged in the case following the arrest of a 21-year-old Indiana man.

Investigators believe Darin Schilmiller posed as a millionaire named 'Tyler' online and offered Brehmer $9 million or more to 'rape and murder someone in Alaska', according to court documents obtained by KTVA.

Cynthia Hoffman, 19, (right) was found dead with a gunshot wound to the back of her head in rural Anchorage on June 2. Her best friend Denali Brehmer, 18, (left) and four other teens were arrested and charged over her murder earlier this month. Photo courtesy of KTVA

Brehmer was allegedly supposed to send photos and videos of the killing back to Schilmiller as part of the plan.

The teenager allegedly agreed to the arrangement and offered four of her friends a cut of the $9 million if they helped.

Investigators believe Darin Schilmiller posed as a millionaire named 'Tyler' online and offered Brehmer $9 million or more to 'rape and murder someone in Alaska'. He was arrested last week on child porn charges

Brehmer told police that she and 16-year-old Kayden McIntosh borrowed a friend's car and drove to the popular Thunderbird Falls hiking trail with Hoffman on June 2.

She told police they had planned to take photos of each other tied up and bound Hoffman's hands, feet and mouth with duct tape.

Brehmer said that at some point, McIntosh took a gun from her and shot Hoffman before pushing her into the river.

They then allegedly drove to a park, called Hoffman's family and said they were dropping her off at the park. Police said they went to another park and burned Hoffman's purse and other items, as well as the gun used in the shooting.

McIntosh is charged as an adult with first-degree murder and evidence tampering. Brehmer is charged with first-degree murder. The owner of the car, Caleb Leyland, 19, and two juveniles, a male and female, are also charged with conspiracy in the case.

The teens told police each of them was supposed to receive a share of Schilmiller's promised reward for their role in the killing.

Brehmer allegedly agreed to Schilmiller's plan involving Hoffman whose nickname is CeCe. Pictured above is an excerpt of text exchanges between the pair in which the murder was mentioned

Hoffman's family said the victim had the mental age of a seventh grader and that she met Brehmer when they were both students at Service High School

The FBI says Schilmiller directed Brehmer to record the sexual exploitation of girls. Text messages (above) on Brehmer's phone show Schilmiller directing Brehmer on how she should assault them

After police obtained a search warrant for Brehmer's phone, investigators say they found child porn, sexually explicit photos and text messages between her and Schilmiller.

Federal prosecutors announced the arrest of Schilmiller on child pornography charges last week.

He is charged with production of visual depiction of minors in sexually explicit conduct and attempted receipt of those depictions.

In a criminal complaint, FBI Agent Jessica Hais said Schilmiller directed Brehmer to record the sexual exploitation of girls.

Brehmer told police she shot video of a girl who was 8 or 9 and another who is 15 and sent them to Schilmiller.

In interviews, she referred to him as 'Tyler' from Kansas.

Hais, who is part of the FBI's Child Exploitation Task Force, said in the criminal complaint that investigators later determined 'Tyler' was Schilmiller.

Kayden McIntosh, 16, and Caleb Leyland, 19, are two of the other teenagers charged earlier this month in Hoffman's death

Text messages on Brehmer's phone show Schilmiller directing Brehmer on how she should assault the older girl, authorities said.

Federal prosecutors in Anchorage say Schilmiller, who is a person of interest in Hoffman's murder, will be extradited to Alaska to face charges.

Hoffman's family said the victim had the mental age of a seventh grader and that she met Brehmer when they were both students at Service High School.

'All I know is that my daughter didn't deserve all this,' her father Timothy Hoffman said when he went to court to see the teenager's arraigned.

He said Cynthia had described Brehmer as her 'best friend'.

He said a developmental disability that caused his daughter to operate intellectually at about a seventh-grade level had made her vulnerable.

'She should have had the friends that she wanted. She shouldn't have had people that wanted to plot against her. And the ages of these people? I think it is sick. And now they don't have to live the nightmare that I have to live,' he said at the time.