Three weeks after the death of Buet student Fardin Noor Parash, the investigators are now considering some new theories as to why he died.
Previously, they focused their investigation on whether Fardin was killed by drug dealers, as some media reported citing unnamed sources in law enforcement.
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They were also probing whether he was murdered by muggers, or if he was killed over a personal feud, but no headway could be made along those lines.
"We are now taking into account several new theories," said Rajib Al Masud, deputy commissioner of the Detective Branch of police (Motijheel), which has been tasked with the investigation.
He, however, declined to disclose details for the sake of the investigation.
Fardin's father Kazi Nuruddin recently said "frustration is growing" in his family as investigators were yet to identify the killer(s) or find the motive.
After tracking his location and analysing CCTV footage, DB said Fardin got into a human haulier from the city's Jatrabari at 2:15am on November 5.
At 2:25am, he got off the vehicle a short distance from the Demra end of the Sultana Kamal Bridge and began to walk in that direction.
Ten minutes later, his phone was switched off.
A large amount of mobile data was spent for about 20 minutes until the phone was turned off, and investigators believe he was listening to music at the time, according to a DB lead investigator who requested anonymity.
Fardin's phone was recovered with his body from the Shitalakkhya in Narayanganj's Siddhirganj on November 7.
His father Kazi Nuruddin previously told this newspaper that he thought his son appeared to be forced to walk in the CCTV footage that investigators had taken from Jatrabari.
Detectives already interrogated the human haulier driver and his assistant who told them that Fardin willingly got in and got off the vehicle, the official said.
Earlier, Rab claimed that they had enough information to suspect that Fardin was killed at Chonpara slum by alleged drug dealer Rayhan Mahmud and his gang.
However, Rab did not say why the victim went to Chonpara.
Amatullah Bushra, a third-year student at a private university, remains the only person arrested in the case filed by Fardin's father as the prime suspect.
Bushra is now behind bars although DB said they did not find her involvement in the killing.
Fardin, a third-year civil engineering student at Buet, was with Bushra until he dropped her off at Rampura at 9:45pm on November 4.
