What does Chattanooga gunman's diary tell us about him?

FBI officials say they have discovered the diary of Chattanooga gunman Muhammad Youssef Abdulazeez.

Days after a gunman opened fire at a Naval Reserve Center in Chattanooga, Tenn., killing five servicemembers, FBI officials have discovered the Chattanooga gunman's diary, which offers a glimpse inside the head of a troubled, suicidal young man who was struggling with substance abuse as well as legal and financial problems.

The diary reveals that 24-year-old Chattanooga gunman Muhammad Youssef Abdulazeez wrote about having suicidal thoughts as far back as 2013, and of "becoming a martyr," after losing a job due to drug abuse, according to a report by ABC News.

The diary, along with information a family representative told ABC, helps paint a clearer picture of Mr. Abdulazeez, who has not yet been connected to any terrorist group, and his motives.

According to reports, Abdulazeez, a naturalized US citizen born in Kuwait, was first treated by a child psychiatrist for depression when he was 12 or 13 years old.

As a child, Abdulazeez, a self-described "Arab redneck," had access to guns, which he used to shoot at squirrels or targets.

As he grew up, he began to struggle with drugs and alcohol. In May 2013, Abdulazeez, an electrical engineering student, lost a job at a nuclear power plant in Ohio after testing positive for both prescription and illegal drugs.

That appeared to be a new nadir for Abdulazeez, plunging him deeper into drugs. Around the same time he was laid off, he began writing about suicidal thoughts and wanting to become a martyr.

"In a downward spiral, Abdulazeez would abuse sleeping pills, opioids, painkillers, and marijuana, along with alcohol," a family representative told ABC News.

Relatives tried to admit him into an in-patient center for drug and alcohol abuse treatment, but insurance would not cover the costs.

In 2014, his family sent the 24-year-old to Jordan for seven months to remove him from negative influences and company in the US, a visit that FBI agents are investigating for possible ties to extremism, though his family insists he was not radicalized there.

Although some reports indicate Abdulazeez returned from Jordan sober, he reverted to his old ways.

Another low point came on April 20, a date celebrated by marijuana users, when Abdulazeez was arrested and charged with drunk driving. According to the arrest records, officers smelled marijuana in the car and saw white powder on Abdulazeez's nose. He said he had snorted powdered caffeine pills.

That arrest was deeply embarrassing for the Chattanooga gunman and sunk him further into depression, according to reports.

Just before the shooting, Abdulazeez was struggling with a job at a manufacturing plant with 12-hour overnight shifts, and was taking sleeping pills so he could fall asleep during the day. He was also thousands of dollars in debt and was considering filing for bankruptcy. And he was preparing for an appearance in criminal court for his DUI.

A family representative told ABC News that Abdulazeez's family had told the FBI that their son was not radicalized, but "was susceptible to bad influences."

"There are no words to describe our shock, horror, and grief," Abdulazeez's family said in a statement. "The person who committed this horrible crime was not the son we knew and loved. For many years, our son suffered from depression. It grieves us beyond belief to know that his pain found its expression in this heinous act of violence."

Like the brown spiral notebook recovered from the belongings of Aurora, Col., shooter James Holmes, a key piece of evidence in a trial that determines whether he was methodical or simply mad, Abdulazeez's diary may also hold important clues about the motives behind the Chattanooga shooting.