Jurgen Roth, a top German journalist, investigating organized crime and mafia in Bulgaria, has stepped up his calls on prosecutors to launch a probe into the country's former interior minister.

"The Bulgarian authorities should do their job and take Rumen Petkov to justice," Roth said in an interview for Deutsche Welle on Thursday.

The statement came after a Bulgarian second-instance court cleared the renowned German publicist, who was sued by the country's former Interior Minister Rumen Petkov over alleged slanders in his book about organized crime in Bulgaria, entitled "The New Demons".

In his book Roth cites sources making scandalous statements that Petkov has relations to organized criminal networks and is involved in the production of synthetic drugs in Bulgaria.

According to high-level unnamed officials in the Interior, quoted by Roth, the former interior minister personally controls the trafficking of amphetamines from Bulgaria to Turkey and the Middle East, which was the practice of the Security Services during the communist regime. Petkov is also said to have met with criminal figures involved in drug production.

Roth has repeatedly harshly criticized Bulgaria's justice system, but now says he is pleased with the verdict and the position of the Bulgarian court.

"Of course I am happy that the Bulgarian court showed respect for the freedom of the press and opinion. But let's not forget that the most important thing now is whether the court will complete its job and investigate Rumen Petkov over the charges against him."

The investigative journalist has repeatedly confirmed that he stands behind every single word that he has written and would have done everything in the same way if he had to write his book today.

If his claims are not slander, they represent serious accusations and Roth says an investigation should be launched.

When approached by Novinite.com a year ago to comment on this issue, the German journalist said:

"In my book, and what I wrote on my blog, I never slandered Mr. Petkov. I only quoted serious people who doubt the reputation of Mr. Petkov. And be sure, that Vanyo Tanov describes very exactly his experience with Mr. Petkov, how the meeting with the so called Galevi-Brothers happened and about the Interference of Rumen Petkov in criminal investigations. It would be also interesting to know what Budemir Milosav Kujovich said about a visit of DANS in prison, to get Vanyo Tanov discredited. And I am sure, if a prosecutor gets this document from the court, he must start an investigation. In Germany this is what would happen. But in Bulgaria?"