The probe into the email purportedly sent by Indian Mujahideen (IM) minutes after the Varanasi blast, appears to be heading nowhere with investigators finding it difficult to establish as to who had sent the mail.
"The culprit had hacked into unsecured WiFi network with a broadband Internet connection to send the mail," a crime branch official said.
"Technically, the IP address from where the mail was sent has been traced to one Talreja family in Navi Mumbai. But, it is very difficult to know who had sent the mail and using which instrument. Whether a laptop, a computer or any other instrument was used to hack into Talreja's WiFi network is also not clear," he said.
The IM is suspected of having hacked into the WiFi network of Akhil Talreja, a resident of Sector 17 in Vashi, and sending the email to media houses, claiming responsibility for the Varanasi blast.
Talreja, a 26-year-old disc jockey, was questioned twice but was later let off by police.
Sources in Mumbai Crime Branch, which is coordinating with the Navi Mumbai police, said they have sifted through the CCTV footage available with commercial establishments in the Sector 17 of Navi Mumbai to identify if any person was found moving suspiciously in the locality.
"This has not helped much. The probe has reached a dead end," the official said.
According to police, the logger of the router has been disabled, so there was no trace of who logged and hacked it.
A gmail ID was used and the mail was written on December 6. The account has been accessed rarely, police sources said.
An FIR was registered at Vashi Police Station against unidentified persons for hacking into unsecured WiFi network in Navi Mumbai and allegedly concealing the existence of a design to wage war against India. The offence is punishable with imprisonment of up to 10 years.