Forensic officials use international phonetic alphabets while recording a voice sample and ask the subject to pronounce only a small part of the original statement so that both vowels and consonants can be analysed.
This inquiry by the United Kingdom government into the 2002 Gujarat violence is covered in the BBC documentary which is now blocked by the government of India. It holds then Chief Minister Narendra Modi, who is now PM, 'directly responsible.'
The anti-Sikh riots of 1984 marks one of the "darkest" years in modern Indian history, a US senator has said, as underlined the need to remember the atrocities committed against Sikhs so that those responsible may be held accountable.