“The films show that she was alone on the starboard and never came back in again,” said Shirley Magné of the City Police to the TT news agency.
“You can see that she disappears. It's a tragic accident that she fell overboard.”
Sarah Lagerström, 22, was on board the Birka Paradise cruise ship which was heading back to Stockholm from Åland in the Baltic Sea.
After a night of partying with her boyfriend, the 22-year-old went out on deck alone at 4am to smoke while her partner slept, wrote the Helagotland newspaper.
She has not been seen since.
When her boyfriend found himself alone in the morning, he assumed his girlfriend had simply joined other passengers and went looking for her.
However, unable to find her, he alerted authorities who immediately checked the boat's security camera footage.
The tapes showed the woman walking out of screenshot and then not reappearing.
The Missing People volunteer organization was on the scene on Monday and Tuesday, together with the woman's family, but their searches proved unsuccessful.
Despite no footage of the actual fall being available, police put together available videos and drew the conclusion on Wednesday that she had likely fallen overboard.
Police are now interrogating possible witnesses, although believe there is no reason to suspect crime, according to the paper.