A potential murder investigation has been launched after a Polish woman and her seven-year-old son plunged from a ferry into the sea, prosecutors say. The pair were travelling from Sweden to Poland when the child fell into the water, Swedish authorities said. His 36-year-old mother jumped overboard in an attempt to save him, they said. The two were later winched to a helicopter and taken to a Swedish hospital but later died. A rescue operation, involving a thermal imaging camera and both Swedish and Polish rescue crews, was launched when the alarm was raised. The Swedish ferry, the Stena Spirit, had been in the Baltic Sea, midway through its journey to Gdynia in Poland from Karlskrona in Sweden when the pair fell, officials said. The country’s prosecution chiefs said on Friday they had launched a preliminary investigation in which the criminal charge was murder, but added that no suspect had been identified. “The investigation aims to try to clarify what happened,” prosecutor Stina Brindmark said. Polish police issued an appeal to passengers asking for information on how the accident happened. The mother was in the water for 59 minutes before being picked up, and her son 66 minutes, Polish website Fakt reported. It said resuscitation was started immediately but the two could not be revived. Police questioned the crew of the ferry to reconstruct events, but officers have not made contact with anyone who saw what happened, according to Fakt. Stefan Elfstrom, spokesman for Stena Line, said someone on the ferry raised the alarm. “Items have been found that belong to these people, but not the people themselves,” he said of the woman and child. “Then the alarm went off, the crew looked at the surveillance cameras and saw that two people had fallen into the water. “There is little information on whether there were relatives or people who knew the two people on the ferry. However, someone noticed that two people were missing.” Confirming the deaths, spokesman Mariusz Ciarka said: “Unfortunately, in the morning we received information from the Swedish side that we have to pass on this terrible news to the family, because both the boy and the woman are dead.” Breaking news: more follows Read More Fear of no end to riots in France after police killing of teen: ‘It’s getting worse’ Where are the French riots and why are they happening? UK issues France travel warning after looting across city - live Fear of no end to riots in France after police killing of teen: ‘It’s getting worse’ Where are the French riots and why are they happening? UK issues France travel warning after looting across city - live