The two bombs that exploded inside sleeper coaches of the Bangalore-Guwahati Superfast Express were powerful explosive devices and could have caused more damage if they had been placed on an elevation, officials familiar with the probe said Friday.

Tamil Nadu Police said that there were some similarities between these bombs and the ones used to target Narendra Modi’s rally in Patna in October, but did not elaborate. They also said they were looking for a man who got off the train from an adjacent coach, and was not seen later.

A preliminary report submitted by Tamil Nadu to the union home ministry suggests that the seats under which the bombs were placed bore the impact of the explosion, and damage from the shrapnel was not widespread.

A woman software engineer was killed and 14 people injured when the bombs exploded after the train had pulled into Chennai Central station Thursday morning. Preliminary examination by the NSG team which visited the site found that the bombs contained ammonium nitrate and traces of potassium chlorate, officials said. The explosives were stuffed in a pipe and connected to a timer.

Tamil Nadu Police CB-CID IG Mahesh Kumar Agarwal told a press conference in Chennai that parts of a clock, batteries, metal pellets and a metallic pipe were recovered. The bombs were placed at an earlier station, he said, adding that the train would have been near the Andhra Pradesh border had it not been running 90 minutes late.

Officials said CCTV footage shows a person who got down from S3 coach at 7.08 am – the blasts were at 7.15 am in S4 and S5 – but did not get back on. However, they termed his movement as only unusual and not suspicious.

Investigators are said to be struggling for clues as pipe bombs can be assembled easily and have been used by several terror groups. Earlier this year, a similar pipe bomb was found under the car of Union minister V Narayanasamy’s son in Pondicherry. The NIA is probing the case and is yet to make a breakthrough. In February, Tamil Nadu police seized pipe bombs from behind a Reliance store in Madurai.

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