Mumbai police investigators tracking the source of at least 17 “threat mails” over the past year to prominent establishments across the city — the stock exchange, courts, five-star hotels and even schools — have dug up a trail that leads all the way to Chennai, The Indian Express has learnt.

Police sources told this newspaper that they believe the sender, or senders, was also on the radar of Chennai police over the past three years with at least 22 cases registered there over bomb threats, including after the stampede at actor-politician Vijay’s rally last month that killed 41 people.

They also suspect that the threat mail last month that led to the Delhi High Court being evacuated briefly originated from the same source.

Investigators have traced several “commonalities” in all th

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