Severin Krasimirov, a Bulgarian national, was detained on suspicion of killing 30-year-old Viktoria Marinova, whose badly beaten body was found in a park in the Danube border city of Ruse on Saturday.
The journalist’s murder shocked her country and prompted claims she may have been targeted as “a warning” because of her work. The European Commission has demanded a rapid investigation to bring her killers to justice.
Mr Krasimirov was later detained in Germany at the request of Bulgarian authorities.
DNA evidence found on her body implicated him in her killing, said Bulgaria’s interior minister, Mladen Marinov.
He said the suspect, a 21-year-old resident of Ruse, had a previous criminal conviction for scrap metal theft.
Investigators have found “no apparent link” to Ms Marinova’s work, the minister added. He said evidence pointed to “a spontaneous attack, not premeditated”.
The television journalist for local station TVN had presented a programme about alleged fraud involving EU funds days before the death.
While Ms Marinova did not appear to have been closely involved in the fraud investigation, her show Detector touched on a sensitive subject in Bulgaria, where corruption is endemic.
Following her killing, the owner of an investigative website that featured on the programme said he had received “credible” information that his journalists were in danger.
“Viktoria’s death, the brutal manner in which she was killed, is an execution,” said Bivol.bg owner Asen Yordanov. “It was meant to serve as an example, something like a warning.”
Bulgarian prosecutors have since launched an investigation GP Group, a large construction firm accused in the programme of embezzlement, and have frozen €14m (£12m) of the company’s assets.
The country’s chief prosecutor, Sotir Tsatsarov, said he could not yet say whether Ms Marinova’s death was linked to her work.
At a press conference also attended by prime minister Boyko Borissov on Wednesday morning, he added Bulgaria expected Mr Krasimirov to be extradited from Germany.
“We are currently following a European arrest procedure. The German prosecutor has arrested the suspect, they will then assess how to proceed,” Mr Tsatsarov said.
Bulgarian authorities have come under international pressure to quickly bring the journalist’s killers to justice.
A spokesman for European Commission president Jean-Claude Juncker said he expected “a swift and thorough investigation” that would “bring those responsible to justice and clarify whether this attack was linked to her work”.
The Committee to Protect Journalists said it was “shocked by the barbaric murder”, calling on Bulgaria to “employ all efforts and resources to carry out an exhaustive inquiry”.
Ms Marinova’s death has also angered many in Bulgaria, where there is public frustration with corruption and an inefficient justice system that has been criticised by the European Commission.