Bulgarian officials say a man named Severin Krasimirov has been detained at their request.
The country’s Interior Minister, Mladen Marinov, said the suspect was a DNA match for evidence recovered at the crime scene.
Current evidence does not suggest the attack was linked to Ms Marinova’s work as a journalist, officials said.
She had recently hosted a TV programme in which two investigative journalists discussed alleged fraud involving EU funds and prominent businessmen and politicians.
However, chief prosecutor Sotir Tsatsarov said the attack seemed to have been a spontaneous sexual assault, adding that all possibilities were still being considered.