Islamabad, Pakistan (CNN) -- A former Pakistani intelligence official kidnapped by militants on his way to the tribal regions has been killed, sources told CNN Friday.
The victim, Khalid Khawaja, was kidnapped with a Pakistani filmmaker and another former intelligence official.
Two military sources and a local administrator in North Waziristan confirmed that the man's body was found in the village of Karam Kot, 25 kilometers (15.5 miles) east of Miramshah, North Waziristan. The sources say he was shot three times in the chest.
A letter thought to be from the captors has found on the body of Khawaja, and Pakistani TV showed still photos of what it said was the body of Khawaja.
"This is Khalid Khawaja who has been working for ISI and the CIA, the biggest enemy of Muslims," the letter said, referring to Pakistan's Inter-Services Intelligence, the country's top spy agency, and the U.S. Central Intelligence Agency.
"He played an important role, on behalf of the ISI and the CIA during the Pakistani Military's siege of the Red Mosque in 2007. Traitors like this will meet the same fate."
It was signed, "From Asian Tigers."
Shumama Khawaja, Khalid's wife, said, "It is true," when asked about the news of his death. He wanted martyrdom, she added.
"In the life of Muslims, this is a precious thing in life. What he wanted, God gave him. I'm the wife of a martyr and I feel proud of my husband," Shumama Khawaja told CNN.
The militants who kidnapped the three people had demanded the release of three Afghan Taliban leaders in return for the release of the three hostages, an Afghan Taliban source told CNN earlier this month.
The source said the kidnapped men would be killed if Afghan Taliban leaders Mullah Abdul Ghani Baradar, Mullah Abdul Kabir and Mullah Mansour Dadullah were not released in 10 days.
Baradar was the No. 2 man in the Afghan Taliban behind Mullah Mohammed Omar before Baradar was captured in Pakistan in February.
Khawaja and Col. Sultan Amir Tarar, the second man abducted along with the film maker, are former members of the ISI. The two were acting as guides for filmmaker Asad Qureshi, who was working on a documentary on militants in Pakistan's tribal region.
Khawaja's son told CNN the three had been missing since March 26. Two video clips earlier this month showed Khawaja and Tarar identifying themselves while sitting in front of a white sheet and holding the front page of an Urdu-language newspaper.
It's not clear what the date of the newspaper is. In one video, Sultan Amir Tarar says: "I was in the army for 18 years and then 11 years in the ISI. On the way here I sought the counsel of General Baig."
In the other video, Khawaja says: "I was in the air force for 18 years, of which two years were with the ISI, and I am here because [of] General Hamid Gul, General Aslam Baig and the ISI's Colonel Sajjat."
Gen. Hamid Gul, known as "the father of the Taliban," served as head of the ISI in the 1980s, during the Afghan war against the Soviets.
Journalist Nasir Dawar contributed to this report