A Moroccan man convicted of helping three of the Sept. 11, 2001, attackers as they plotted to strike New York and Washington was flown from a Hamburg jail on Monday to the city's airport in preparation for his deportation to his home country.

Mounir el-Motassadeq, who was convicted in 2006 of membership in a terrorist organization and accessory to murder for his part in the plot, was expected to be put on a flight later in the day to Marrakesh, Morocco.

The 44-year-old was flown by helicopter to the airport, and then escorted from the helicopter by two heavily armed police officers to another helicopter. It took off shortly after, presumably to take el-Motassadeq to a larger airport for the international flight to Morocco. Blindfolded with hands and ankles in shackles, he was then led by two police officers to another helicopter while other heavily armed police in balaclavas patrolled the area and watched from rooftops.

Authorities wouldn't comment on the operation for security reasons.

"Mr. Motassadeq will leave the country soon," Hamburg Interior Ministry spokesperson Frank Reschreiter told The Associated Press. "All the necessary procedural steps for this have been ticked off according to plan."

It wasn't immediately clear what would happen to him in Morocco.

El-Motassadeq's lawyer, Jan Jacob, refused to comment on the case.

Denied knowing Hamburg cell's intentions

El-Motassadeq was convicted of being part of the so-called Hamburg cell, including Mohamed Atta and fellow Sept. 11 pilots Marwan al-Shehhi and Ziad Jarrah.

German courts ruled that el-Motassadeq was aware the three planned to hijack and crash planes, even though he might not have known the specifics of the plot. They said el-Motassadeq had helped "watch the attackers' backs and conceal them" by doing things such as helping them keep up the appearance of being regular university students paying tuition and rent fees, and transferring money.

El-Motassadeq acknowledged training at an al-Qaeda camp in Afghanistan, but insisted he knew nothing of his friends' plans to attack the U.S.

"I swear by God that I did know the attackers were in America," he shouted in accented German at a sentencing hearing. "I swear by God that I did not know what they wanted to do."

Originally arrested in Hamburg in November 2001, el-Motassadeq was convicted in 2003 of membership in a terrorist organization and thousands of counts of accessory to murder — taking into account victims on the ground — to become the first person convicted anywhere on charges related to Sept. 11. He was sentenced to the maximum of 15 years in prison.

Moroccan Mounir el-Motassadeq is escorted at Hamburg airport as he is released from prison in Hamburg after serving a 15-year jail sentence for helping hijackers plot the Sept. 11, 2001, attacks on U.S. targets. (Fabian Bimmer/Reuters)

However, a Federal Court overturned that verdict in 2004, largely because of a lack of evidence from al-Qaeda suspects in U.S. custody, and sent the case back to Hamburg.

After a 2005 retrial, el-Motassadeq was again convicted of membership in a terrorist organization that included Atta, al-Shehhi and Jarrah. But he was acquitted of being an accessory to murder after the court ruled it didn't have enough evidence that he knew of the hijackers' plot.

El-Motassadeq was sentenced to seven years in prison at the time, but was freed in early 2006 until his appeal could be heard.

Later that year, the Federal Court reversed the Hamburg court's acquittal of el-Motassadeq on the accessory to murder charges. It limited the number of counts, however, to the 246 people killed aboard the airplanes and the 15-year sentence was restored.