UPDATE: Man Released From Custody Over Bulgarian Journalist's Death

UPDATE: Bulgarian police have released a man they arrested in connection with the killing of investigative journalist Viktoria Marinova.

A Romanian man has been released from police custody after facing questioning for 24 hours over the death of the TV reporter.

Danube Regional Police Chief Teodor Atanasov earlier told media they were trying to establish his alibi.

"Our work is continuing. For the time being there are no facts and circumstances that we can announce," Atanasov said.

The man has since been released without charge as the European nation faces mounting international pressure to bring the person responsible to justice.

Local media are reporting another man has been arrested in connection to the crime after attempting to flee to Germany, however police are yet to confirm any further arrests have been made.

The 30-year-old mother of one who was TV reporter for a local news station was found brutally raped and murdered in a park near her home town of Ruse.

On her last aired TV show just a week before her death, Marinova interviewed two journalists who were investigating alleged corruption involving EU funds.

Source; Getty Images

Officials said they have yet to establish any link between Marinova's work and her death, and have not ruled out that it could have been a random attack, local media reported.

READ MORE: TV Journalist's Rape And Murder Sparks Outrage 

But her death has sparked anger across the country with her colleagues reportedly demanding protection from police in the wake of her death, claiming they now fear for their own safety.

International organisations have also called for Bulgarian authorities to act swiftly, with the European Commission demanding a thorough investigation to bring those responsible to justice.

"There is no democracy with a free press," it tweeted.

The Commission's Vice President Frans Timmermans said he was shocked by the horrendous murder.

"Again a courageous journalist falls in the fight for truth and against corruption."

The U.S. embassy in Sofia has also offered its assistance to local authorities for help in bringing those responsible to justice.

Bulgaria has fallen to 111th place in the 2018 World Press Freedom Index and has ranked last among all EU nations, according to Reporters Without Borders.

Image: Reuters

Earlier this week hundreds of mourners gathered for a candlelight vigil laying flowers and lighting candles for the slain journalist, while others took part in an organised community marathon which covered the length of track where her body was discovered.

Marinova leaves behind a young child, who is believed to be seven-years-old.

With AAP.