Police said the victims hands and feet had been bound with aluminum wire. Their heads were covered with plastic while their bodies were wrapped in bed sheets.
Police have yet to identify the victims.
An unidentified source from the provincial police office said the four victims might have been wealthy individuals. The bed sheets used to wrap the bodies appeared to be very expensive. He said the victims appeared to have been killed at least two days before their bodies were found in the riverbank. He said the head of one of the female victims appeared to have been bashed in with a hard object. Mannag said some residents saw a green van going to the river on the night of April 14.