New Delhi (CNN) -- A man from India died in Pakistan early last week from a beating he took in jail there days before. The day after his passing, a Pakistani inmate received a beating in an Indian prison.
He died Thursday, a government official in India said. Some are calling it a revenge attack, something that CNN cannot confirm.
Sarabjit Singh was incarcerated in Lahore, after a Pakistani court convicted him of spying for India in connection with terror attacks in Pakistan in 1991. Singh's family has maintained he was innocent.
He was sentenced to death.
Late last month Singh was hurt in "a scuffle with fellow inmates," according to Pakistan's foreign affairs ministry. The apparent dust up was intense enough to put him into a coma.
When he died in a hospital, India's government expressed "great anguish" over the violence.
"This was, put simply, the killing of our citizen while in the custody of Pakistan jail authorities," the Indian Ministry of External Affairs said in a statement.
"The criminals responsible for the barbaric and murderous attack on him must be brought to justice," demanded Indian Prime Minister Manmohan Singh in a statement.
India's media erupted with indignation.
"India outraged over Sarabjit's murder" read a headline in The Pioneer.
"Sarabjit Singh butchered by our enemies," read another in The Times of India.
There were claims that the death row inmate's killing had been planned and reports that his organs went missing after his death.
Pakistan's ministry of foreign affairs confirmed there was an autopsy. It is not unusual for a pathologist to remove organs in the process.
The postmortem revealed that Singh had died of cardiac arrest on May 2, caused by the trauma he had suffered, Pakistan's foreign affairs ministry said.
On May 3, Pakistani citizen Sanaullah Ranjay was attacked in an Indian jail in Jammu and transferred in critical condition to a hospital in Chandigarh.
After days in a coma, he passed away Thursday.
"He had multiple organ failure due to severe head injury," the hospital said in a statement.
Pakistan's foreign affairs ministry reacted to Ranjay's death with indignation.
"The brutal manner in which Sanaullah was attacked in the jail is most unfortunate and a matter of deep concern for the Government of Pakistan," the ministry said in a statement.
Like their counterparts in India, they, too, demand an investigation into the prison killing and that the "perpetrators of this heinous crime be brought to justice."
There has been little media resonance about the Pakistani inmate's death in India.
Singh's remains have already been returned to India, where he was cremated, media there have reported.
According to Islamic custom, the body of a deceased person should be buried within 24 hours of death.
Indian and Pakistani diplomats have said they are in communication about transferring Ranjay's remains back to his native town of Sialkot in Pakistan.
History of strife
Although ties between New Delhi and Islamabad have improved since tensions flared in the aftermath of the 2008 terrorist attacks in Mumbai, the two deaths put a fresh strain on their delicate relations.
India and Pakistan have fought several wars since their independence from British colonial rule more than 65 years ago.
Though some may assume so, it is not yet clear if Ranjay's killing was revenge for Singh's. Many men have died of violence in jails.
CNN's Jethro Mullen, Shaan Khan and Saima Mohsin contributed to this report