The reason for the fire which gutted the 32-storeyed Sagar Sangeet residential tower’s cap in Colaba and killed Rajnish Behl, 75, Bollywood legend Nutan’s husband, is still a mystery.The fire which started at 11.15 pm on Tuesday in Behl’s 31st floor house and spread to the top floor, was doused only by 10.30 am on Wednesday using more than eight water tankers.It was a herculean task, made impossible by the residential society’s laxity. ‘‘The fire-service inlet was corrugated, the staircase was quite narrow,’’ P.D. Karkopikkar, assistant divisional officer of the Mumbai Fire Brigade who is investigating the case, said. Starting the building’s power pumps took a long time, and water could not be pumped even upto 100 metres. Finally, the fire brigade assembled their own pumps.Fire officers said the residents were lucky. ‘‘If the fire had been somewhere on the floors below, people would have been trapped. The staircases are so narrow,’’ said a fire brigade official.Mohnish Behl stayed with his family on the 32nd floor while his father stayed on the 31st. The entrance to Mohnish’s flat was through his father’s flat. A friend of Mohnish said: ‘‘On reaching his father’s flat, he saw smoke and fire and called for him. When there was no response, he thought his father must have left. It was only when he came down and did not see his father did he realise that he was trapped inside.’’A message was soon sent to the fire officers. However, with so much delay in starting the pumps, Rajnish Behl could not be saved.