NEW YORK - A Florida doctor on trial for pledging to help al Qaeda had hoped to convince a jury that he did not know he had offered his medical expertise to the terror group.

But jurors Monday apparently did not believe him. They convicted Dr. Rafiq Abdus Sabir of providing material support to terrorists by agreeing to treat injured al Qaeda fighters so they could return to Iraq to battle Americans.

"By the time I was done, I knew he was guilty," said juror Jeffrey Ellsworth of Brewster.

Sentencing was set for Sept. 12.

Sabir, 52, was convicted in Manhattan federal court after a three-week trial that featured testimony from him and Ali Soufan, an FBI agent who posed as the al Qaeda recruiter in a sting operation that led to four arrests.

When the verdict was read, Sabir looked straight ahead. Later, as he was escorted from the courtroom, he waved to supporters, who said, "Stay strong."

"We are deeply disappointed in the verdict," said Sabir's lawyer, Ed Wilford. "It is another example of the erosion of constitutional rights we suffered post-9/11."

The charges against Sabir, including conspiracy to provide material support to terrorists, carry a potential maximum sentence of 30 years in prison.

The verdict came after jurors heard audio tapes of a May 2005 ceremony in a Bronx apartment in which Sabir and his best friend, Tariq Shah, a martial arts expert and jazz musician, pledged loyalty to al Qaeda and, the government alleged, Osama bin Laden.

Shah pleaded guilty just before the trial to providing material support to a terrorist organization and agreed to serve 15 years in prison, though he has not been formally sentenced.

A Brooklyn bookstore owner who pleaded guilty after the sting operation was sentenced to 13 years in prison. A Washington, D.C., cab driver has pleaded guilty and agreed to serve 15 years in prison.

Sabir, of Boca Raton, Fla., testified at trial that Shah never told him he was talking with an al Qaeda recruiter. At the pledge ceremony, Soufan mispronounced al Qaeda more than a dozen times, Sabir said. He also said he did not know "sheik Osama" meant bin Laden.