What we know about Ikaika Kang, the US soldier arrested on terror charges

— -- Army Sgt. Ikaika Kang, the active-duty serviceman based in Hawaii who allegedly said he wanted to "kill a bunch of people," also sympathized and worked with people he believed were connected to the terror group ISIS, court documents charge.

Here is what we know about Kang, his personal beliefs and his alleged affinity for terrorism, based on the affidavit filed in U.S. District Court in Hawaii Monday in support of his arrest.

The affidavit -- written by an FBI special agent who is assigned to the Honolulu, Hawaii, office as a counterterterrorism investigator -- is based on "personal observations, training and experience, and information obtained from investigative FBI agents, witnesses, and FBI investigative materials," according to the document.

Birney Bervar, Kang’s court-appointed defense attorney, said his client may suffer from service-related mental health issues, declining to elaborate, The Associated Press reported.

A veteran, MMA enthusiast and trained fighter

Kang, who the FBI said was taken into custody on Saturday on charges of providing material support to ISIS, was deployed to Iraq for nearly a year before also serving eight months in Afghanistan, the affidavit states.

He was deployed to Iraq from March 2010 until February 2011, and Afghanistan from July 2013 to April 2014, according to the affidavit.

In the military, Kang, 34, served as an Air Traffic Control Operator, the affidavit notes.

The document states that he was also both a fan and participant in Mixed Martial Arts (MMA), which is a combat sport popularized in no small part by The Ultimate Fighting Championship (UFC), a burgeoning league that gathers top-ranked fighters from across the world.

He also received formal combat training through the military, achieving "Level IV Tactical Combat Instructor" status, which was the highest level of training available to him, according to the affidavit.

Kang allegedly wanted to pour Drano into a man's eyes over a grudge

The affidavit said that Kang has had a history making threatening statements, beginning in 2011, and that he was reprimanded on several occasions for threatening to hurt or kill other service members.

In March of this year, he allegedly told someone that he had been conducting research on YouTube about "the most effective and painful ways people had been tortured," the affidavit states.

He told the same person that he was angry at a civilian who had taken away his air traffic controller's license, and that he wanted to tie the man down, and pour Drano into his eyes, according to the affidavit.

Kang viewed terror groups as oppressed

The affidavit describes what it says are Kang's evolving thoughts about ISIS.

He allegedly told someone in late-March that he once thought of the group as "bloodthirsty," "baby-eating" killers but changed his thinking after researching their ambitions, according to the affidavit.

The context for the research he conducted was figuring out "what to do in case he was put in a position where he had to submit to ISIS," according to the affidavit, and it led him to conclude that they were "really just a group that strongly believed in their interpretation of the Muslim religion, and if you did not agree, you would die."

He told the same person a few days later that he wanted to get a job to go overseas and help "oppressed people," the affidavit states.

Kang said that people "like to put labels like al Qaeda and ISIS" on certain groups, but he just considered them to be oppressed, according to the affidavit.

Allegedly worked for ISIS as recently as last week

Kang, according to the affidavit, was heard saying "that he now wanted to take his rifle, his magazines, and ‘kill a bunch of people’" as recently as July 8.

Also in July, Kang bought a Go-Pro Karma drone with a Go-Pro camera and accessories to give to ISIS in support of their fight, splitting the cost with someone else to get it, according to the affidavit.

The affidavit alleges that Kang explained how the drone might "allow ISIS fighters to escape a battle involving U.S. tanks" by giving them a clearer view of both U.S. tank positions and potential ISIS escape routes.

The purchase of the drone built on previous efforts to help ISIS's cause, including preparing a PowerPoint presentation and also agreeing to attend training courses in May of this year, according to the affidavit.

Kang also attempted to turn over military information to someone he believed to be a member of ISIS in June, the document notes.

He had been under investigation by the U.S. Army and the FBI for over a year prior to his arrest, according to an FBI spokesman, who said he had shown explicit signs of radicalization dating back to last summer.

Such signs of radicalization caused the Army to formally refer his case to the FBI in August of 2016, according to the affidavit.

Kang argued "pro-ISIS views while at work and on-post," according to the affidavit.

He's now the first active-duty service member to be charged with material support for ISIS, according to Seamus Hughes of the GWU Extremism Tracker.

He is also included among the 128 people who have been charged in the United States with offenses related to ISIS since March of 2014, according to that University's research -- the same year the group proclaimed itself to be a worldwide caliphate.

ABC News Luis Martinez and Tara Fowler contributed to this report.