(Reuters) – A U.S. Army sergeant described by former colleagues as a one-time “model soldier” is due to be sentenced in a Hawaii federal court on Tuesday after pleading guilty to providing material support to the Islamic State militant group.

Ikaika Erik Kang, 35, agreed to a plea deal in August on four counts of breaking anti-terrorism laws in which he accepted a proposed sentence of 25 years in prison.

Kang had begun expressing support for Islamic State, designated by the United States as a foreign terrorist organization, by early 2016, according to the U.S. Department of Justice.

Undercover agents from the Federal Bureau of Investigation began meeting with Kang earlier this year, some of them posing as members of the militant group.

Kang gave them military gear and classified documents and agreed to teach them hand-to-hand combat in a video-recorded session he thought would be used to train other Islamic State fighters, according to federal prosecutors.

Lawyers for Kang filed three letters of support in court on Monday that described him as a diligent but withdrawn soldier who struggled with his mental health.

Kang’s older sister, Erika Takahashi, wrote that Kang grew up in a “very abusive household.”

“I do not know when things got like this for my brother but I know he is a good person on the inside,” she wrote.

Two soldiers who worked with Kang in air-traffic control at Alabama’s Fort Rucker military post wrote to Judge Susan Oki Mollway, urging her to help Kang get counseling.

Thomas Maia, who was Kang’s first supervisor at Fort Rucker, called Kang a “model soldier” but said he had worried about Kang’s odd behavior. This included staring at a wall for hours on end, saying he was trying to listen to the sound of his blood running through his veins, Maia wrote.

Maia wrote that his efforts to secure a mental health evaluation for Kang were rebuffed.

“He didn’t seek out ISIS on his own, he was approached and socially engineered by the FBI at the Army’s request,” Maia wrote, using an acronym to refer to the Islamic State. “If he would have been given adequate mental treatment back when I asked for it, none of this would have happened.”

Federal prosecutors say Kang agreed to swear an oath of loyalty to Islamic State in a pseudo-ceremony organized by the undercover FBI agents. After the ceremony, Kang told the agents he was ready to take his rifle to downtown Honolulu and start shooting, whereupon he was arrested.

(Reporting by Jonathan Allen in New York; Editing by Scott Malone and Bernadette Baum)