Taliban spokesman Zabiullah Mujahid said in a statement released Monday that Obaidullah Akhund died on March 5, 2010.

He was one of the top deputies of the Taliban leader Mullah Mohammad Omar, Mujahid says the man’s relatives are just now getting confirmation he died of heart disease in a Karachi prison.

Obaidullah was arrested in early 2007 in Balouchistan, which borders southern Afghanistan. At the time, he was the highest-ranking Taliban figure to be captured since the fall of the hardline regime in 2001.

The Taliban say they want Pakistani officials to provide details about his arrest, incarceration and death.