Mumbai, July 20 (IANS) A week after triple bombings in India's financial and entertainment hub killed 20 people, investigators were Tuesday still grappling for clues leading to perpetrators of the biggest terror attack in India since the November 2008 siege of this city.


The only headway, at least on record, has been a sketch of a suspect drawn on eyewitness accounts, and CCTV footage recorded at Zaveri Bazar, Opera House and Dadar West -- the three sites of the July 13 blasts that injured scores including over 120 who were hospitalized.

The sketch is being circulated among the dozen probe teams and would be compared with existing police records of suspected terrorists, according to officials.

The investigation has led to one death. A young man picked up for questioning in Mumbai died within hours, with the family alleging that he was tortured to death. Police have ordered an inquiry.

Mumbai Police have admitted that the attackers remain unknown. But what they have been able to discern is that the improvised explosive devices were made of ammonium nitrate, fuel oil and ball bearings.

They were triggered by timer devices, but the exact make of the detonators is another mystery for forensic experts.

Identification of the timer devices is crucial because it may establish a pattern and trace similarities, if any, to previous terror attacks.

Once known, this would give the investigation a definite angle and maybe point to the outfit behind the blasts.

The investigators, according to a police official, were still examining the voluminous CCTV footage recorded on 11 CDs to check out the details of individuals in each frame for possible suspects.

Usually, CCTV cameras capture 25-30 pictures or frames per second, which makes the job of examining the footage tedious. Particularly so, when the footage is from a crowded place.

The probe has been expanded to various parts of the country.

So far, no one has claimed responsibility for the blasts. Police officials, who say they "keeping all options open", have refrained from naming any particular suspect.

But raids have been conducted at various places for suspected Indian Mujahideen operatives.

According to Maharashtra Anti-Terrorist Squad (ATS) chief Rakesh Maria, teams have gone to Gujarat, Karnataka, Andhra Pradesh, Madhya Pradesh, Uttar Pradesh, West Bengal and New Delhi.

"The investigations are proceeding in a certain direction and we are confident of a breakthrough soon," Maria said Monday.

Many suspected Indian Mujahideen activists, arrested for their alleged involvement in previous attacks, were interrogated in jails for possible clues into the latest Mumbai bombing.

But success in cracking the latest terror whodunit seems elusive, with no known progress on the probe.