New evidence obtained by British broadcaster BBC raises questions about the Greek coast guard's version of events surrounding last week’s tragic sinking of a fishing boat crammed with migrants which left at least 79 dead and many more missing.

The boat capsized and sank off southwestern Greece early Wednesday. While more than 100 passengers were rescued, nearly 500 are missing in the surrounding waters of the Mediterranean Sea, according to UN officials.

The BBC has obtained computer animation of tracking data from MarineTraffic, a maritime analytics platform.

An analysis of the movements of other vessels in the vicinity based on the data indicates that the overcrowded fishing boat had been stationary for at least seven hours before it overturned. This contradicts the Greek coast guard's assertion that the boat was heading towards Italy and did not require assistance during that time.

In light of the new information, however, the United Nations has called for an investigation into Greece's handling of the disaster. There are concerns that more decisive action should have been taken earlier to initiate a comprehensive rescue operation.

Greek officials maintain that those on board the vessel said they did not want help and were not in immediate danger until moments before their boat sank.