DHAKA, Bangladesh

Delwar Hossain Sayedee, vice president of the opposition Jamaat-e-Islami party and a former member of Bangladesh’s parliament, died Monday night in custody.

Sayedee, 83, a prominent Islamic scholar and speaker in Bangladesh, was taken to Bangabandhu Sheikh Mujib Medical University (BSMMU) in Dhaka on Sunday afternoon after suffering a heart attack.

He had been in prison for 13 years and was facing several health complications and passed away at the hospital while undergoing treatment, Brig. Gen. Md Rezaur Rahman, the director of BSMMU, confirmed to the media.

Thousands of Jamaat supporters began gathering at the hospital and chanting slogans against the government for keeping him in prison in “false” cases and due to “motivated” court verdicts.

Sayedee had been serving a life sentence for alleged crimes against humanity during the Bangladesh Liberation War.

His party, however, considered the trial controversial and regarded it as part of a political attempt to try party leaders.

In a condolence message, the party said “a grave injustice has been done to him by imprisoning him for life in a false and fabricated case.”

In 2013, a local court called the International Crimes Tribunal sentenced Sayedee to death for crimes against humanity. At least 78 people died in clashes with police and other law enforcement agencies across the country in an immediate reaction to the court verdict.

The country’s Supreme Court in 2014 reduced the punishment to life imprisonment, however.

The crimes tribunal, set up in 2009, has been criticized by global rights groups for not following fair trial standards. Since then, it has delivered verdicts against over 130 people in over 50 cases.

Bangladesh gained independence from Pakistan in 1971 after a bloody war that lasted for months. The Jamaat-e-Islami party has been criticized for its alleged collaboration with the Pakistani army during the war.