Maria Ladenburger, the daughter of a high-ranking EU official, was returning from a party in the university city of Freiburg in Germany when she was assaulted on a cycle path.
She was raped and then drowned before her body was found in the River Dreisam.
The shocking incident happened on October 16 but details have only been released after an arrest on Friday.
The suspect, an Afghan migrant, was caught after police found DNA on a scarf near the path.
The scarf reportedly belonged to Maria.
They also found a strand of hair on a nearby blackberry bush.
Officers then trawled CCTV to see find people with a similar hairstyle, which led them to the suspect.
Following his arrest the suspect, aged 17, pleaded guilty to the attack and will be sentenced next year.