Washington - Former US president George W Bush and a raft of senior officials from his administration should be investigated for conspiracy to torture and for other crimes, Human Rights Watch (HRW) said on Tuesday.In a scathing report, the international rights group decries the lack of prosecutions of those involved in the Central Intelligence Agency's secret programme to torture detainees in the wake of the September 11 2001 attacks.It said there is enough evidence for the attorney general to order criminal probes.The 153-page report outlines evidence to support the main criminal charges that could be brought against those behind what is referred to so-called "enhanced interrogation" techniques, and challenges claims that prosecutions are impossible."US officials who created, authorised and implemented the CIA programme should be among those investigated for conspiracy to torture as well as other crimes," the report summary states.It lists several top Bush officials, including the former president himself, then CIA director George Tenet, former attorney general John Ashcroft and former vice president Dick Cheney.Additionally, the report says James Mitchell and Bruce Jessen - who devised the programme under a CIA contract - should also be investigated for their roles in the initial conspiracy.'War on terror'The American Civil Liberties Union last month sued the two psychologists on behalf of a group of former prisoners from the early days of America's "war on terror".The CIA's use of torture was detailed in an explosive report released a year ago that describes the agency's interrogation of al-Qaeda suspects, including beatings, rectal rehydration and sleep deprivation. Such mistreatment was more brutal than had been previously acknowledged - and did not produce useful intelligence."It's been a year since the Senate torture report, and still the Obama administration has not opened new criminal investigations into CIA torture," said Kenneth Roth, executive director of Human Rights Watch."Without criminal investigations, which would remove torture as a policy option, Obama's legacy will forever be poisoned."Human Rights Watch said that although much of the abuse took place a decade or more ago, statutes of limitation do not preclude criminal charges."The statute of limitations for the crime of conspiracy may be extended if those responsible conceal a central component of the plot, which was the case with the CIA programme," the group said in a statement.Under the UN Convention against Torture, ratified by the United States in 1988, governments are meant to investigate allegations of torture."The failure to investigate and prosecute CIA torture increases the danger that some future president will authorise similar illegal interrogation methods in response to an inevitable serious security threat," the group said.Republican presidential hopeful Donald Trump recently called for the return of waterboarding, a simulated drowning interrogation technique widely denounced as torture, saying it was "peanuts" compared to what the Islamic State group is doing.