(CNN) -- A Cuban prisoner who went on a hunger strike because he was not part of the government's recent mass pardon has died, a human rights leader said Tuesday.
The prisoner, Rene Cobas, died Sunday of a heart attack, after authorities at the Boniato Prison, near Santiago, disregarded a doctor's recommendation that he be moved to a provincial hospital, said Elizardo Sanchez.
Sanchez, who heads island's independent Commission for Human Rights and National Reconciliation, said his group plans to investigate whether the military authorities at the prison were criminally negligent in their inaction.
Cobas had gone on strike immediately after President Raul Castro announced the latest round of amnesty on December 23. Cobas called the pardons "exclusive and limited," Sanchez said.
The decision to release 2,900 prisoners followed "numerous requests" from their family members and religious institutions, and was a humanitarian gesture, Castro said last month.
He cited the upcoming visit of Pope Benedict as one of the motivations behind the move, which he said showed the "generosity and strength of the revolution."
The pope has said he plans to visit Mexico and Cuba before Easter.
Among those were to be freed were prisoners over the age of 60, along with those who were sick, female or young with no previous criminal record.
With some exceptions, prisoners convicted of spying, terrorism, murder and drug trafficking would not be released.
In 2010, Castro agreed to free 52 prisoners arrested during a 2003 crackdown on political dissidents.
That pardon was prompted by the death of a jailed dissident, Orlando Zapata Tamayo, following an 80-day hunger strike protesting inmate conditions.