The threat that sent alarm bells ringing in the security establishment was later declared as a hoax.
The bomb threat emails received by around 150 schools in Delhi-NCR early this month are suspected to have been sent from Hungary's capital Budapest, Delhi Police officials said on Tuesday.
According to an official, the IP address of these emails has been traced to Budapest and Delhi Police will soon be contacting its counterpart in Hungary for further investigation.
The IP (internet protocol) address is a unique identifying number assigned to every device connected to the internet.
The mail purportedly sent from a mail.ru server claimed that explosives were planted on the school premises, triggering massive evacuations and searches as panic-stricken parents rushed to pick up their children on May 1.
The threat that sent alarm bells ringing in the security establishment was later declared as a hoax as nothing objectionable was found from the school campuses.
The police, after filing an FIR into the case, had written to the mailing service company 'mail.ru' based in Russia via Interpol.
The police were investigating the IP address used to send the e-mails, besides the sender and origin of the mail to decipher the conspiracy and motive behind the bomb hoax that resulted in panic across Delhi-NCR on Wednesday.
The officials said an initial probe has led to the suspicion of a "deeper conspiracy" hatched by a terror group during the ongoing Lok Sabha polls, adding that the threat mail could have been sent by an ISIS module.
(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)