Hasina was at her residence in Dhaka, known as the Ganabhaban, for the duration of the call which took place on 18 July, a source with knowledge of the leaked audio told the BBC. It was a crucial moment in the demonstrations. Security officials were responding to public outrage at police killings of protesters captured on video and shared across social media. In the days following the call, military-grade rifles were deployed and used across Dhaka, according to police documents seen by the BBC. The recording the BBC examined is one of numerous calls involving Sheikh Hasina that were made by the National Telecommunications Monitoring Centre (NTMC), a Bangladeshi government body responsible for monitoring communications. The audio of the call was leaked in early March this year - it's unclear by whom. Since the protests, numerous clips of Hasina's calls have appeared online, many of them unverified. The leaked 18 July recording was voice matched by the Criminal Investigation Department in the Bangladesh Police with known audio of Sheikh Hasina's voice. The BBC conducted its own independent verification by sharing the recording with audio forensics experts Earshot, who found no evidence the speech had been edited or manipulated and said it was highly unlikely to have been synthetically generated. Earshot said the leaked recording was likely to have been taken in a room with the phone call played back on a speaker, due to the presence of distinctive telephonic frequencies and background sounds. Earshot identified Electric Network Frequency (ENF) throughout the recording, a frequency that's often present in audio recordings due to interference between a recording device and mains-powered equipment, an indicator that the audio has not been manipulated. Earshot also analysed Sheikh Hasina's speech – the rhythm, intonation and breath sounds - and identified consistent noise floor levels, finding no evidence of synthetic artefacts in the audio. "The recordings are critical for establishing her role, they are clear and have been properly authenticated, and are supported by other evidence," British international human rights barrister Toby Cadman told the BBC. He is advising Bangladesh's International Criminal Tribunal (ICT), the court hearing cases against Hasina and others. An Awami League spokesperson said: "We cannot confirm whether the tape recording referenced by the BBC is authentic."