Two leading human rights groups on Thursday accused Egyptian authorities of failing to conduct an impartial and transparent investigation into the suspicious death of an economic researcher in custody. In a joint statement, Human Rights Watch and Amnesty International accused Egyptian prosecutors of having turned a blind eye to “mounting evidence” that 48-year-old Ayman Hadhoud disappeared, was tortured, and was denied access to timely healthcare. Hadhoud’s whereabouts were unknown for two months before he was pronounced dead in April. The Interior Ministry said then that he had died in the go…