Amid conflicting claims on who was behind Wednesday's Delhi high court bombing, a third e-mail surfaced on Friday claiming responsibility for the terror attack.
It was sent to the Delhi Police and home minister P Chidambaram said it was written "amateurishly", but was being taken seriously by investigators.
"Third e-mail arrived today (Friday)," Chidambaram said, elaborating that it was written "amateurishly" in a numerical code that was deciphered "easily".
"Number 1 reads as A, number 8 reads as H. It seems it is hinting at the next target," he said, adding that Ahmedabad in Gujarat may have been named as the next target.
He said it seemed that the communication "has not been sent by a serious person", but investigators were nevertheless taking it seriously.
"We have sent revised advisories to states, including Gujarat," the minister said.
This is the third e-mail sent in as many days since the deadly bombing outside the Delhi high court on Wednesday which killed 13 people and injured over 90.
The earlier e-mails were attributed to the Pakistan based Harkat-ul-Jehadi Islami (HuJI) and the home grown terror group Indian Mujahideen, which owned up to the bombing.
The HuJI e-mail was tracked to an internet cafe in Jammu and Kashmir's Kishtwar district. It threatened to carry out more such attacks if the death penalty to 2001 parliament attack convict Afzal Guru was not immediately repealed.
Chidambaram said the sender of the HuJI e-mail has been identified and taken into custody. But he did not elaborate.
"The person suspected of sending the e-mail has been taken into custody for interrogation. We will have to wait for the report (after questioning of the suspect)," he said.
Police had earlier picked up the owners of the cafe.
A TV network received the second e-mail in which the Indian Mujahideen said it had plotted the attack and warned that its cadres would strike outside a shopping complex on Tuesday.
Meanwhile, sleuths led by the National Investigation Agency (NIA) are pursuing scattered leads to crack the case, but have not achieved any major breakthrough.
Chidambaram said the investigators were not in a position to say if the blast was the handiwork of Pakistan-based terrorists.
"I cannot say if it's the Indian module or the module from across the border," the minister said.