Charge: Seattle high school student extorted girl for sex The defendant allegedly threatened to publish explicit images of the victim if she did not comply

A 20-year-old man allegedly extorted a girl into repeatedly performing sexual acts for him starting when they both attended Chief Sealth International High School in West Seattle, according to prosecutors. less A 20-year-old man allegedly extorted a girl into repeatedly performing sexual acts for him starting when they both attended Chief Sealth International High School in West Seattle, according to ... more Photo: Vstock LLC/Getty Images/Tetra Images RF Photo: Vstock LLC/Getty Images/Tetra Images RF Image 1 of / 1 Caption Close Charge: Seattle high school student extorted girl for sex 1 / 1 Back to Gallery

A 20-year-old man allegedly extorted a girl into repeatedly performing sexual acts for him starting when they both attended Chief Sealth International High School in West Seattle, according to prosecutors.

The harassment and coercion persisted for about 15 months between late 2013 and early 2015, police reports say.

Prosecutors charged Fernando Martinez-Mancha last month with second-degree extortion. Seattle police believe he may be connected to additional sexual assaults of other high school students.

The relationship between Martinez-Mancha and the student one year his junior was revealed to school authorities in late January 2015 when the girl wrote an essay for a class about the extortion and assaults, police reports indicate. The teacher verified with the girl that the story was true and reported the matter to a school counselor, a mandatory reporter who called police.

The girl, then 17, showed police text messages from Martinez-Mancha, which "clearly showed [Martinez-Mancha] harassing and cyberstalking her," according to Seattle police.

The student told police she was afraid of going to and from school because Martinez-Mancha might find her and force her to talk to him. She repeatedly told him to leave her alone.

The harassment began on an occasion in November 2013 -- when she was 16 and the defendant was 17 -- in which Martinez-Mancha reportedly gave the girl marijuana and demanded oral sex from her if she did not have money to pay for it, reports indicate. She ultimately performed oral sex on him, but later discovered that Martinez-Mancha filmed the encounter and continued to demand more sexual acts to keep him from posting the footage on social media, police reports say.

Despite her telling him that she did not want to do drugs or have any kind of contact with him, he persisted in his threats, compelling her to occasionally meet his demands, according to detectives' accounts. He reportedly ordered her to see him once a month and later offered to pay her for the sexual acts.

Martinez-Mancha lived a block away from her family and the girl was afraid of her parents finding out about the incidents, she told detectives.

Martinez-Mancha allegedly claimed to have "19 other girls" he also "made deals" with, according to court records.

Previous Seattle police reports document other victims at Chief Sealth being touched on their genitals by Martinez-Mancha without their consent and despite their attempts to escape his grasp. The students were in special education classes with Martinez-Mancha and had "diminished (mental) capacity," court documents say.

Martinez-Mancha spoke with Seattle detectives in February 2015 and admitted to having sexual encounters with the girl who reported him and that he recorded each meeting, police reports indicate.

He also admitted to threatening to post pictures and footage of them, but claimed that he texted "JK" -- "just kidding" -- during their text exchanges.

During the course of the investigation, the case changed between detectives' hands, delaying the case's submission to prosecutors, Seattle Police Department Spokesman Sean Whitcomb confirmed last week.

Martinez-Mancha was booked into King County Jail Dec. 19 and released soon thereafter on a conditional release.