Osama bin Laden's son Omar has called on the US to provide proof of his father's death. Osama bin Laden's adult sons have attacked the legitimacy of the US assault that killed their father, calling for a UN inquiry to determine why he was not arrested and prosecuted. In a joint letter the family said it wanted to know "why an unarmed man was not arrested and tried in a court of law so that truth is revealed to the people of the world". "Arbitrary killing is not a solution to political problems," they said. The letter was sent to the New York Times under the name of Omar bin Laden, the 30-year-old fourth son of Bin Laden who lived with the al-Qaida leader in Sudan and Afghanistan but has publicly denounced his attacks on civilians. Drawing comparisons with Saddam Hussein and the former Serb leader Slobodan Milosevic, the statement said "international law has been blatantly violated" and, in a reference to the shooting of other people in the compound, said President Obama had ordered "the execution of unarmed men and women". The letter contained some contradictions. Bin Laden called on the US to provide proof of his father's death "we are not convinced" he said while also condemning Osama bin Laden's sea burial as a deprivation of the family's religious rights. Bin Laden also said it was "unworthy" of US special forces to kill an unarmed female family member and one of Osama bin Laden's sons, identified in news reports as 22-year-old Khalid. But the exact identities of those killed remains unclear. Some reports last night suggested that another son, 20-year-old Hamza, had escaped the raid. A senior Pakistani intelligence official said he had no information about any escapees. Bin Laden's family said it was calling on Pakistan to repatriate his three wives and several children, who are being held in military custody after surviving the dramatic US special forces raid on their Abbottabad home eight days ago. Washington has publicly demanded access to the wives, one Yemeni and two Saudis, saying they may offer new intelligence on al-Qaida. Officials in Islamabad responded with conflicting statements but last night the interior minister, Rehman Malik, told CNN that access would be granted although he not specify when. In 2007 Omar bin Laden married Jane Felix-Browne, a parish councillor from Cheshire whom he met during a holiday to Egypt. She later changed her name to Zaina Mohamed al-Sabah. In the statement Bin Laden reiterated that he "always disagreed with our father regarding any violence and always sent messages to our father, that he must change his ways and that no civilians should be attacked under any circumstances". "Despite the difficulty of publicly disagreeing with our father, he never hesitated to condemn any violent attacks made by anyone, and expressed sorrow for the victims of any and all attacks." Bin Laden said he was assembling a "panel of eminent British and international lawyers" to help obtain answers. If the Obama administration did not respond within 30 days it would take "necessary action" including lodging cases with the international criminal court and the international court of justice.