The judges — Paul G. Gardephe and Reena Raggi — commented as they heard arguments in an appeal by Mustafa Kamel Mustafa to a three-judge panel of the 2nd U.S. Circuit Court of Appeals.

Mustafa was convicted in Manhattan federal court in 2014 of supporting terrorist organizations by ensuring there were satellite communications for kidnappers during a 1998 attack on tourists in Yemen, of supporting plans to open an al-Qaida training camp in Bly, Oregon, and sending someone to an Afghanistan training camp. Four hostages were killed in Yemen.

Mustafa, who was extradited to the United States from England in 2012, is serving a life sentence. In the 1990s, he led London's Finsbury Park Mosque, reportedly attended by Sept. 11 conspirator Zacarias Moussaoui and shoe bomber Richard Reid. Mustafa denied meeting them. At trial, he was referred to by his alias, Abu Hamza al-Masri.

On appeal, defense attorney Sam Schmidt did not deny that his client spewed hateful speech that was "anti-Jewish, anti-West and anti-American." But he said Mustafa did not urge those who attended training camps in Afghanistan to do so with the intent to carry out acts of terrorism.

He found the appeals judges most receptive when he argued that the jurors were improperly told that Mustafa had been convicted in Great Britain on solicitation-to-murder charges. Mustafa was convicted in early 2006 in London Central Criminal Court and was sentenced to seven years in prison.

Gardephe, a district court judge temporarily sitting on the appeals court, questioned Assistant U.S. Attorney Ian McGinley at length about whether the U.S. jury was ever told that solicitation to murder has a different meaning in the United Kingdom than in the United States.

He noted that Mustafa's conviction in England related to hate-speech charges rather than an effort to directly solicit anyone to commit murder, which is the more common meaning in U.S. courtrooms.

"Why wasn't it important for the jury to understand that?" Gardephe asked.

McGinley said it was "somewhat clear to the jury" that Mustafa's convictions in the United Kingdom related to his speech rather than killings. And he said Mustafa opened the door to mention of his United Kingdom convictions by misleadingly implying during his testimony that he was in custody there solely on the U.S. charges and by portraying himself as a peacemaker.

Raggi said it seemed there was "nothing to prevent the jury from thinking" the charges related to murder.

If the judges conclude jurors were told about the convictions improperly, it is unclear whether they would order a new trial. They could decide that it would not have affected the verdict and allow the conviction and sentence to stand. Historically, the 2nd Circuit has upheld the outcome of terrorism trials.