The grounded oil tanker drifted from Oman coast to the city's Juhu-Versova beach in July last year.
According to officials, they failed to trace the route because of the weather conditions between June-August and said the route will always remain a "mystery".
"We wanted to reconstruct the route with the help of satellite imagery, but at that time monsoon was prevalent and the entire area was covered with clouds. We are, therefore, not successful in tracing the route," said an official from the Directorate General of Shipping.
Also, no one even spotted this vessel drifting or else we would have alerted concerned authorities, the official said.
After the vessel ran aground at Juhu, an investigation was launched to ascertain the cause of it getting adrift unmanned to the shores of Mumbai.
The ship had started drifting off Oman coast on June 29 due to engine failure and ingress of water in the engine room.
All the 13 Indian crew members were rescued by a warship before it finally ran aground on July 31. The ship was later moved to Dabhol Port.