A glimpse of a tall and dark man with curly hair climbing the staircase was the sole clue that led to the arrest on Thursday of one of the killers of Ajay Agarwal. The only son of a Burrabazar-based businessman was murdered in his Surya Sen Street apartment in north Calcutta on June 18.

In a pre-dawn raid on Thursday, the alleged murderer was arrested in his ancestral home of East Midnapore and Rs 1.76 lakh ? part of the money looted from Agarwal?s apartment after the murder ? was seized.

Madan Hatui, alias Lambu, the arrested employee of a roadside eatery close to the building where the Agarwals live, confessed to police.

?He told us how he had robbed the money and murdered Ajay with the help of another employee of the eatery,? said Damayanti Sen, deputy commissioner (special), detective department. ?We are looking for Madan?s accomplice who has been at large from the day of the murder.?

The body of Ajay, a Class XII student of a prominent English medium school in north Calcutta, was discovered, with his throat slit, by his father Anil Agarwal around 7.45 pm. His hands and feet were tied, and Rs 3 lakh was missing from one of the almirahs.

The needle of suspicion initially pointed at three friends of Ajay who had spent two hours with him in the flat and left a few minutes before the murder.

?We questioned them repeatedly and told them to recount every moment when they were coming out of the flat. On the first two days, their statements yielded nothing,? said an officer of the detective department?s homicide wing.

One of Ajay?s friends finally came up with a vital lead. ?He said he had seen a man in his late 20s climbing up the staircase leading to Agarwal?s apartment around 1.40 pm. The friend crossed the tall and dark man on the staircase,? said the officer.

Madan told police that he, along with his accomplice, killed Ajay because he had recognised them.