The 27-year-old woman, identified as Moumita Das, and her 24-year-old companion Avijit Paul had arrived in Dehradun on Oct 21 to celebrate Diwali, but were reportedly missing after two days, Vikasnagar Circle�Officer Swapan Kishore Singh.
The four accused, including the cab driver Raju, Bablu, Guddu and Kundan, have confessed of raping, murdering and robbing the two victims, he added.
The incident happened on October 23 when the victims were returning in the taxi from the Tiger Falls about 30 km from Chakrata near here.
"They first strangulated Paul, then raped her. They also robbed them before disposing of their bodies at two different places," he said.
The matter came to light after Paul's body was recovered from Purola in Uttarkashi district and identified, Singh said.
Das was pushed into the Yamuna river near Lakhamandal whereas Paul was pushed off a cliff about two kms away from there, the official said.
The couple did not surface for several days prompting woman's father to lodge a case in Delhi on October 29 in this connection, Singh said.
Search has been launched to scour the girl's body from the Yamuna.
Moumita Das taught at a school in Gurgaon, whereas Avijit Paul was a resident of Dumdum in Kolkata.
All the four accused are being interrogated further in the matter, he said.