Jamshedpur police who had so long suspected the death of DBMS English School student Fardeen Khan to be a case of suicide are now investigating a possible murder.

The 16-year-old boy's father and two uncles were summoned to Bistupur police station for questioning late on Wednesday night while cops are analysing CCTV camera footage available from Beldih Lake area. They have also decided to procure the call detail record (CDR) of Fardeen's smartphone and have stepped up hunt for the missing gadget.

The Class X student's body had been found floating in the lake, near his Dhatkidih home, on Monday, a day after he went missing. Fardeen had received a call around 3am on Sunday after which he had left home.

DSP (control room) Sudhir Kumar admitted that they had started a murder probe based on the FIR lodged by the boy's father, Shamsher Khan, an employee of a steel manufacturing company in Qatar.

"Our priority is to get and analyse the CDR of Fardeen's phone. Once the last caller is detected, we may have a vital lead into the mysterious death of the teenager," Kumar said.

The DSP said they had already studied a camera footage focussing on an alley near Fardeen's house. "The footage shows a youth talking on his phone at 2.40am. But, it is not Fardeen. We have to find out who the youth is and what he was doing around the victim's house at that hour."

The senior officer conceded that retrieving Fardeen's missing smartphone had become important at this juncture. "We are thinking of engaging a diver to locate the cellphone, which may have slipped out of the boy's pocket when he fell/was thrown into the waters. We have gauged the depth of Beldih Lake. It is around 25ft."

A source at Bistupur police station said besides father Shamsher Khan, Fardeen's uncles Gulrez Khan and Firoz Khan had been questioned on Wednesday. Their fourth brother, Pervez Khan, was not present at his rented house in Dhatkidih and hence, could not be summoned to the thana. "Cops also visited the dead boy's home in Dhatkidih Block B to speak to female members of the family," the source added.

Anwar Ali, Shamsher's brother-in-law and yet another uncle of the victim, said Fardeen's mother Yasmin Khan had last seen her only son around 1.35am on Sunday. "The boy was still awake and fidgeting with his phone. She asked him to go to sleep. Two hours later she found him gone," Anwar said.

Principal of DBMS English School Rajni Shekhar said Fardeen was an average student, but friendly by nature.

"Other students hadn't found anything odd in his behaviour when he last attended school on Friday," she added.