Pointed out Deputy Commissioner of Police (zone 3) Sunil Paraskar, recordings can prove to be vital evidence in organised crimes like extortion, where there are neither eyewitnesses nor complaints by victims. Preservation of recordings of correspondence conducted through agencies like the Mahanagar Telephone Nigam Limited (MTNL) could cement gaping holes in several investigations, he added.

Most officers are unaware of the procedures to be followed in tape recording and its usage and admissibility in the court of law, observes Mendonca in the circular. Only thatevidence where the conversation is relevant to the issue and where there is identification of the voice in the recording is admissible, says the circular. The recording becomes legal evidence only when it is corroborated with the statements of the person who deposes that he or she carried out the conversation in question with the other person. A third person's deposition that he or she overheard the recorded conversation between the two persons is also admissible.

The Chief Justice and other judges of the Bombay High Court, with the approval of the Governor, had, under section 227 of the Indian Constitution, recently laid down rules for producing a tape recorded conversation in court: the party that produces the tape recorded evidence in court will also produce a transcript of the recording. This will be verified by the court, and the tape itself will be kept under the court seal.

Further, the notice of the production of the tape and transcript will be served on the accused through the court, and aninterested party can apply for playing of the tape recording. But, the tape would be played within hearing distance of an officer appointed by the court for this purpose, and as far as possible, in the presence of the other side, says the circular. However, the tape will not be played more than twice without the court's permission, because repeated playing could affect its audibility.

In criminal cases where the appeal lies with the High Court and when the recording is not in English, police should provide an official English translation. The tape will be treated as a separate exhbit and a record of instances when the seal on the tape was opened has to be maintained. Tape recordings also have to be sealed to nullify chances of tampering, adds the circular.