Sami Al-Arian, the former University of South Florida professor who pleaded guilty last spring to aiding a terrorist group, was found guilty of contempt on Thursday for refusing to testify in another terrorism-related case and could serve as many as 18 additional months in prison, The St. Petersburg Times reported.

Mr. Al-Arian pleaded guilty in April to providing services to Palestinian Islamic Jihad, an anti-Israel terrorist group. After a six-month trial in 2005, a federal jury found Mr. Al-Arian not guilty of eight of the most serious terrorism-related charges brought against him, but deadlocked on nine other counts. Before Thursday’s contempt ruling, Mr. Al-Arian had less than 18 months left to serve in prison.

According to the Times, Mr. Al-Arian had been summoned to appear before a grand jury last month to answer questions about a Virginia organization that had given money to his Florida think tank. Mr. Al- Arian refused, asserting that his plea deal nullified any obligation on him to cooperate with the government. The presiding judge disagreed.