Delhi High Court blast investigators battling for conclusive leads to crack the case are now facing a fourth email, sent by 'Chotoo', who has repeated the claim that it was the Indian Mujahideen and not the Harkat-ul-Jehadi Islami who were behind the attack.

On September 8, Thursday, was the first email from 'Chotoo' who claimed it was the IM and not the Harkat-ul-Jehadi Islami (HuJI) who were behind the Delhi High Court blast.

The third email, from IM, was traced to a server in Moscow. It claimed responsibility for Wednesday's terror attack that claimed 13 lives and injured over 90 in the heart of the capital.

The mail also warned of another 'cruel attack', possibly in Ahmedabad.

Home Minister P. Chidambaram said the message was written 'amateurishly' but was being taken seriously by the government.

Meanwhile, sleuths led by the National Investigation Agency (NIA) were pursuing scattered leads to crack the case but have not achieved any major breakthrough.

Home Minister P. Chidambaram has admitted that leads followed so far were 'not conclusive'.

"We found there are promising leads, I can't say they are very conclusive leads. These are being pursued round the clock with help of other agencies, abroad too."

"After the first email, another email arrived and a third arrived today (Friday). These are not being dismissed, although the third one appears to be a very amateurish mail," Chidambaram told reporters, elaborating that it was written with some numerical code pointing towards the next target.

The email warns that the next attack (on Ahmedabad) 'will be so cruel that you people won't be able to forget it for decay (decade)'.

"I just want you to pass a message to the Indian government that if you are willing to know the next attack it is 1,8,5,13,4,1,2,1,4. Till you come to know what it stands for, the next blast will be done. If you have any question get back soon because we don't have time for anything."

The email sender identifies himself as Ali Saed el-Hoori and the message was sent from the killindia@gmail.com ID, according to the sources.

Sources said that the email may have been been sent from a proxy server having the address in the Russian capital.

"The third has been traced to Moscow. The NIA (National Investigation Agency) is not sure whether it was sent by proxy server or it is from Moscow indeed," a source revealed.

A proxy server keeps computers behind it anonymous, mainly for security reasons and to circumvent regional restrictions.

The earlier emails 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 email 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 email has been taken into custody for interrogation. "We would like to wait for that report to come."

The Kashmir police identified the suspect as Mohammad Sayeed who has admitted that he had sent the email from Global Internet Cafe in the town.

The second email, also attributed to the Indian Mujahideen, said the outfit had plotted the attack and warned that its cadres would strike outside a shopping complex on Tuesday.