For weeks, the people of Iceland, a small Nordic country where the police do not usually carry guns and murders are exceedingly rare, have been horrified and riveted by the mysterious killing of a young woman.

The mystery of what happened to the woman, Birna Brjansdottir, an outgoing 20-year-old sales assistant, now appears to have been at least partly solved. She died from drowning after she was thrown — possibly from a bridge — into the North Atlantic Ocean, according to an autopsy report that was leaked Monday night to the national broadcaster RUV.

Ms. Brjansdottir was alive when she was thrown, the report concluded, but it was not clear if the killer knew that, or if she was conscious.

Medical examiners found bruises on her neck, the broadcaster reported, and she was naked when her body was discovered near a lighthouse about 20 miles southeast of Reykjavik, the capital.