Three bodies identified
They are Md Khokon, 35, of Dharampur, Razu Ahmed of Balukhopa in Comilla district and Jahangir Hossain of Chandipur in Jhenidah district.
The identity of other person could not be traced.
For all latest news, follow The Daily Star's Google News channel. They were involved with an outlawed party, police suspect.
According to local people, Khokon, Jhangir, Razu and another unknown persons went to the house of one Abdul Kuddus at Boluhar on Wednesday. They were friends of Kuddus who is also involved with the outlawed party.
On Thursday night, Kuddus took them to his father-in-law's house at the same village and had dinner there.
Later, they left for Dhaka by bus at about 11:00pm, but were ambushed on the way, police suspect.
The killers strangled them and left their bodies on railway line at Pallar field.
Police are still in dark about the motive of the killing.