Tamil Tigers leader Velupillai Prabhakaran was tortured by the Sri Lankan military before being killed, a leading human rights body said in a report released on Wednesday.
The University Teachers for Human Rights (UTHR) quoted high-level military sources as saying that Prabhakaran was tortured in the presence of "a Tamil government politician and a general".
The torture, it said, took place probably at the headquarters of the army's 53 Division, which battled the Liberation Tigers of Tamil Eelam (LTTE) before crushing it last month.
"Several army sources have said that Prabhakaran's (younger) 12-year-old son Balachandran was killed after capture. Our (sources) said that he was killed in front of his father," said UTHR, which has always been critical of excesses both by the military and the LTTE.
"These sources added that this information is correct unless officers at the highest level are fibbing to one another.
"Our sources in addition to several others have said that all the LTTE persons remaining in the NFZ (No Fire Zone) were massacred," it added in a 48-page report, an advance copy of which was made available to IANS.
Sri Lanka announced on May 18 that Prabhakaran, founder leader of the LTTE, was killed in a lonely coastal stretch in the northeastern district of Mullaitivu where the Tigers had massed their forces before going down.
His body was put on display, placed on a stretcher, the back of the head blown off.
Sri Lankan minister Vinayagamurthy Muralitharan alias Karuna, a former confidant of Prabhakaran, had said that the LTTE chief was shot dead with 18 of his guards.
Prabhakaran's death marked the end of the LTTE's dragging conflict that claimed 90,000 lives since 1983.
UTHR said: "Information seeping into the public domain from within the army points to capture or surrender, but the official responses dismissing this are a rehash of stories that public no longer finds credible. It is left to an impartial enquiry to answer this and related questions."
UTHR pointed out that the government was evasive about the fate of Prabhakaran's wife Mathivathani.
It quotes a brigadier as saying: "We had to look for Prabhakaran's body because the world was interested in seeing it. But the body of his wife is not of any importance to us."
The UTHR report said: "That would be the fate of the unknown hundreds of civilians and militants killed in those last days (of fighting)."
According to the report, among the LTTE leaders who surrendered to the army included Baby Subramaniam, a member of the group since 1976 and one of Prabhakaran's oldest associates.
Others reportedly now in government custody included former eastern province political leader Karikalan, former spokesman Yogaratnam Yogi, former head of the LTTE international secretariat Lawrence Thilakar, political advisor V. Balakumar, Jaffna leader Ilamparithi and Trincomalee political leader Elilan.