A deluge of terror-related images used by prosecutors scared jurors and influenced them to convict a Massachusetts man of trying to help al-Qaida, the man's lawyer argued to a federal appeals court Tuesday.

Tarek Mehanna of Sudbury was sentenced to 17 1/2 years in prison after being convicted in 2011 of four terror-related charges and three charges of lying to authorities.

During Mehanna's trial, prosecutors said he traveled to Yemen for training in a terrorist camp and intended to go on to Iraq to fight U.S. soldiers. When that plan failed, Mehanna returned to the United States and disseminated materials online promoting violent jihad, prosecutors said.

In arguments before the 1st U.S. Circuit Court of Appeals, Mehanna's lawyer, Sabin Willett, said prosecutors showed 28 images of the World Trade Center in flames on Sept. 11, 2001, and numerous terror-related videos and repeatedly made references to Osama bin Laden in an attempt to prejudice the jury against Mehanna.