Many high level Iranian officials should be charged for the shooting down of a Ukrainian commercial airliner in January 2020, a UN human rights expert has said, describing the killing of the 176 people aboard as a “profound and serious indictment” of the country’s civil and military authorities. Agnès Callamard, the UN special rapporteur on extrajudicial, summary or arbitrary executions, delivered a 45-page letter to the Iranian government which was made public on Tuesday, outlining her findings from a six-month investigation into the disaster, and complaining about the lack of Iranian cooperation, which has left many of her questions unanswered. Callamard issued a particularly strong condemnation of the Tehran government’s treatment of the victims’ families, who she said had been harassed and threatened, denied the return of remains and personal effects, and forced to go along with officially staged “martyr” funerals. Ukraine International Airlines flight PS752 was shot down by an Islamic Revolutionary Guard Corps (IRGC) air defence missile battery shortly after it took off from Tehran’s international airport, at a time of high tensions, five days after a US drone strike killed an IRGC commander, Qassem Suleimani. The plane was bound for Kyiv but had 55 citizens and 30 permanent residents of Canada aboard. After denying responsibility for several days, Tehran said the Boeing 737-800 was shot down by mistake by an air defence crew who mistook it for an incoming US missile. “The inconsistencies in the official explanations seem designed to create a maximum of confusion and a minimum of clarity. They seem contrived to mislead and bewilder,” Callamard, said in the letter, which was sent to Tehran 60 days ago with a set of questions but has yet to get a reply. The Iranian mission to the UN did not respond to a request for comment on Tuesday evening. “At best, what we have here is an extraordinarily incompetent succession of actions ... to such an extent that they would be in my view, in a criminal court, be described as criminal and reckless,” Callamard told the Guardian. She added that the downing of the plane was a “profound and serious indictment of Iran, both military and civilian authorities, in terms of the violations of their human rights obligations”. The official Iranian account details a series of technical breakdowns and human errors that led to the tragedy, but Callamard said they just raised more questions that Tehran had failed to answer. For example, the official account said the mobile missile unit that fired the two Russian-made Tor missiles that brought down the airliner had not been properly calibrated, so the radar systems showed the aircraft as incoming rather than outbound. Callamard said she had not been given any explanation as to why this miscalibration happened, why it had not been detected, or why it had led to the missiles being fired. It was also unclear why the crew had not followed standard operating procedures that would have prevented the launch, why the airport had not been closed at a time of high tension and why the investigation was botched. The crash scene was looted and bulldozed before international inspectors arrived. There have been conflicting reports about the arrest and prosecution of the missile crew, but Callamard said: “In terms of accountability, unfortunately we cannot expect Iran to charge those at the top or even the middle of the chain of command, and there are many high-level officials who should be charged.” There was no evidence, she added, that Iran had made the fundamental changes necessary to give the rest of the world assurance that the same mistakes would not be made again. Callamard’s letter lambasts the Iranian government for the treatment of the bereaved families. In many cases, personal items went missing after the looting of the crash site and baggage. “Iranian officials sought to coerce families into publicly declaring their support for the government or risk the non-return of their loved ones’ remains,” the letter said. “Many families were reportedly also denied private funerals. Victims were declared ‘martyrs’ who died for their country. As a result, funerals were heavily controlled.” The inscription “congratulations on your martyrdom” was placed on the coffins of the victims against the wishes of the families, the letter added. Families in Iran and Canada, it said, had been received death threats for being critical of Iran. Callamard told the Guardian the treatment of grieving families was “cynical, cruel and criminal”. She said she hoped that international efforts, in particular by Canada and Ukraine, would not be bought off or held hostage by the desire to salvage the 2015 nuclear deal with Iran. Callamard said: “Under no circumstances should the search for justice for PS752 be impaired by the equally important search for a nuclear deal.”