BAY SHORE, N.Y. -- A young New York man caught boarding a plane on his way to Yemen to fight with an al-Qaida affiliate is a mixed-up teenager who was diagnosed with autism and didn't understand the gravity of what he was doing, his attorney told The Associated Press.

Justin Kaliebe, 18, pleaded guilty in a secret federal court proceeding in February to a charge of attempting to provide material support to a terrorist organization. He was ordered to undergo a psychiatric evaluation before he is sentenced Sept. 27. His condition could be considered in determining his sentence; he faces up to 30 years in prison.

"Justin Kaliebe is a gentle, misguided, autistic teenager who does not have the ability to fully understand the magnitude and consequences of his actions," defense attorney Anthony La Pinta said in a statement to the AP.

La Pinta, who joined the defense team after the guilty plea was entered, said he has medical documents showing that Kaliebe was diagnosed with autism as a young child, but he would not release them.

Authorities have declined to say why the plea was entered in secret, though the move could mean Kaliebe was cooperating in the investigation when it was at a sensitive stage.

Kaliebe, who converted to Islam about three years ago, apparently was swept up in the New York Police Department's ongoing investigation into the activities of Muslims throughout the region. Counterterrorism agents and NYPD officers intercepted him on Jan. 21 as he tried to board a flight to Oman at John F. Kennedy International Airport on his way to Yemen.

Acquaintances, including the imam at a Long Island mosque he frequently attended, have described him as emotionally immature and a child of divorce who seemed in need of psychiatric counseling.

According to court papers, Kaliebe told an undercover operative pretending to be a confidant, "There is no way out for me. ... The only way out is martyrdom."

The NYPD has long had an interest in converts to Islam as part of its efforts to prevent terrorists attacks, saying in a 2007 report that they are "particularly vulnerable" to radicalization and "have played a prominent role in the majority of terrorist case studies and tend to be the most zealous members of groups."

Around 2008, the police department stepped up efforts to monitor converts. The department began to look at people who changed their names to ones that sounded Arabic or who came to the United States from Muslim countries, according to police documents obtained by the AP. The program was supposed to be a tripwire in the search for homegrown terrorists, even though it involved monitoring behavior protected by the First Amendment.

Court records don't mention why Kaliebe first came to the attention of the NYPD. But former NYPD informant Shamiur Rahman told the AP in an interview last year he infiltrated a Brooklyn mosque where Kaliebe prayed and was told to watch Kaliebe and another man because they were converts to Islam.

Prosecutors allege Kaliebe began plotting to join al-Qaida on the Arabian Peninsula in 2011 while he was in contact with an undercover operative, who recorded their conversations. The operative told Kaliebe he was from Yemen and could give him pointers on how to get there, according to a criminal complaint.

Kaliebe asked the operative "to assure him that he was not going to 'rat him out' and after the (operative) assured him that he would not, Kaliebe indicated that he wanted to join a group 'for the sake of Allah,'" documents show.

A 20-year-old college student, Ahmad Deib, said he befriended Kaliebe at a mosque in Bay Shore, on Long Island. The two met in about 2010.

Deib said he doesn't believe Kaliebe was capable of terrorism.

"That, to me, is a bunch of garbage," he said. "This is a case of entrapment. This kid, he couldn't hurt a fly. He is one of the most kindhearted kids you would ever know."

Friends said Kaliebe's home life was not ideal. His parents were divorced in 1998 when he was just a toddler, said Bilal Hito, who helps run a youth program at the Long Island mosque.

"There was something about Justin that made you feel you were around a little boy," Hito said. "Mentally he was very young. He was more like a kid brother."

Deib said Kaliebe once stayed at his house for a week because of the strife at home. At the time, Deib said his friend had confided that he had stopped taking antidepressants because he didn't like the way they made him feel.

The young man frequently complained about his home life and appeared to be depressed, imam Abdul Jabbar said in an interview at the Bay Shore mosque. Kaliebe even asked the imam if he could live in the mosque.

He said he advised Kaliebe to seek counseling at school, but the teenager declined, saying he feared being stigmatized.

La Pinta disputed reports that his client had a lousy home life. He said that for the past several years, Kaliebe has lived with his father in Bay Shore. The teenager's mother is remarried and lives in a waterfront community in nearby Babylon.