A Canadian teen who pleaded guilty to terrorism-related charges in connection with a plot to attack New York City landmarks has met in prison with Alberta lawyer Dennis Edney, who previously defended Omar Khadr, CTV News has learned.

Nineteen-year-old Abdulrahman El Bahnasawy’s parents asked Edney, who represented Khadr, a former Guantanamo Bay prisoner, to look at the case, CTV’s Glen McGregor reported Tuesday.

Edney's involvement suggests the family may intend to question the fairness of arresting a young person with addiction issues and possible bi-polar disorder in a scheme an FBI agent helped co-ordinate.

Newly released letters from defence lawyers and a New York prosecutor, filed with a U.S. court, show El Bahnasawy suffered from drug addiction and mental health issues.

The letters say the teen from Mississauga, Ont., suffered a relapse in prison and tested positive for a prescription drug used in opioid-addiction treatments.

"He has a long history of drug use, drug treatment, and relapse," his lawyers, Sabrina Shroff and Clay Kaminsky, wrote in a letter to a judge as they argued for the court to restore his family visits.

El Bahnasawy has been in U.S. custody since the FBI arrested him in New Jersey in May, 2016.

Details of his guilty plea in what has been described as an ISIS-inspired plot to target New York City landmarks only recently came to light, after American court records were unsealed.

The other two accused in the case have been identified as Talha Haroon, a 19-year-old U.S. citizen residing in Pakistan, and Russell Salic, 37, from the Philippines.

U.S. authorities allege the three men plotted to carry out bombings and shootings in heavily populated areas of New York City during the Islamic holy month of Ramadan in 2016.

The documents allege El Bahnasawy purchased and arranged to have bomb-making equipment, including 18 kilograms of hydrogen peroxide, shipped to an undercover FBI agent posing as an ISIS supporter online.

Despite mentions of his mental health issues in court documents, El Bahnasawy told a judge he felt well mentally and physically when he pleaded guilty. He was deemed mentally competent to enter the plea.

Last year, a B.C. judge tossed out the verdicts in the case of a couple found guilty of terrorism charges, saying that the RCMP entrapped them and manipulated them into carrying out a police-manufactured crime. However, American courts are generally more permissive.

El Bahnasawy is scheduled to be sentenced on Dec. 12, 2017.

With files from The Canadian Press