Concrete walls, ditches, guard dogs and spring-gun contraptions: a 1,400-kilometer-long "death zone" formed the inner-German border. Until 1989, it forcibly prevented people from fleeing the GDR. Many people hoped to flee via other countries along the Iron Curtain. Like Bulgaria, for example. A holiday paradise for some, the gateway to freedom for others. But what few knew: The border to Bulgaria was also strictly guarded, even with the use of weapons.

Historian Christopher Nehring did research in Bulgarian archives between 2011 and 2012. He currently works as research director at the German Spy Museum in Berlin. DW spoke with him about the cooperation between the German and Bulgarian state security police before the fall of the Berlin Fall and the killings at the border.

DW: Why is it so difficult to determine the exact numbers of GDR citizens killed in escape attempts via Bulgaria?

Christopher Nehring: There is no central directory, and one probably did not exist even back then. The files are very scattered. You have to search for a long time — and new cases could appear at any time. Also, for years, people tried to avoid as much as possible producing files about any killings. That means that especially in the 1950s and 1960s, only a few files were created or they were destroyed before 1990.

After the fall of communism, those responsible in the Ministry of Defense and the Ministry of the Interior did not have much interest in examining and recording the cases. The most reliable figures are only rough estimates announced by the Bulgarian Minister of the Interior and the Minister of Defense in 1992. They spoke of 339 killings during escape attempts in the years from 1946 to 1985. That means figures are missing for up to five years.

Read more: Dangerous escape: Fleeing the GDR through Bulgaria

How were the killings justified in the files?

In all the files I have found that are about a death, the course of events is very standardized. There are usually only two sentences which are specifically formulated in such a way that they fit into the legal scheme. As early as the 1950s, the law permitted the use of firearms when someone tried to cross the border and resisted.

And one finds this argument in every single file. The military prosecutor's office became involved after a killing at the border, but on the basis of the law it stopped the proceedings against the guards responsible and said that the shootings had been done lawfully. The files then always state that the perpetrator resisted and did not surrender — and was therefore killed.

Although it was so dangerous, for a long time there was a rumor in the GDR that the Eastern Bloc border in Bulgaria was easier to cross than the inner-German border. Where did that come from?

I have always wondered this myself and when I have talked about it in public, people who went on vacation to Bulgaria at that time told me that it was merely word of mouth. To this day, it is difficult to understand how that rumor started.

At the beginning of the 1960s, an article about the Bulgarian border appeared in the West German press which revealed that the information was false: It was very fatal to believe that the Bulgarian border was easy to cross. Even before the construction of the Berlin Wall, it was severely guarded.

I haven't been able to find out the exact origin of the rumor. Probably the good experiences with the locals during vacation gave the impression that Bulgaria was more friendly and lax than the GDR. In addition: The landscape at the Bulgarian border was sparsely populated. It was assumed that it was easy to cross over. A dangerous mistake. Sometimes a deadly mistake.

What did the East German authorities know? And how did the cooperation between the German and Bulgarian state security services generally work?

The working relationship goes back to the beginning of the 1950s. But the subject of escape is very interesting because it did not become a topic for the GDR until the summer of 1962. But even as early as 1958, the Bulgarian state security asked the German state police to send operational staff to Bulgaria. Bulgaria repeated this request again in 1961 — before even construction on the Berlin Wall began.

But it was not until the following year, after the number of escape attempts via Bulgaria had increased so much, that the GDR authorities reacted. It took until the end of the 1960s for the cooperation to become well-established and more effective. From the end of the 1960s onwards, the number of successful escapes via Bulgaria also fell sharply.

The first recorded death of a GDR citizen at the Bulgarian border was in 1965, the last in 1989 — only a few months before the fall of the Berlin Wall, 19-year-old Michael Weber was shot dead. What happened to the bodies of the people killed?

Until the mid-1970s, the bodies were buried by the border troops directly on site in Bulgaria. Only a brief report was sent to the GDR. In the mid-1970s, when the Federal Republic of Germany and the GDR signed treaties for the first time and international pressure on the GDR increased, the Bulgarian authorities began to transport every corpse from the border area to Sofia. Then the GDR embassy had to decide what would happen to the body: whether the relatives would be allowed to see it and whether it would be transferred or not.

Read more: 'Balloon' depicts miraculous escape from the GDR

When I talk to former GDR refugees, there is always talk of horrendous sums that the Bulgarian border guards were allegedly paid for every prisoner. Some speak of 1,000 Marks — at that time an extremely high amount. Is that true?

That would be as much as the Bulgarian Minister of the Interior officially earned at the time. If the military soldiers at the border were really given so much money, then they would have shot anything that moved.

The Bulgarian state security agency certainly offered rewards, but also punishment. For successfully prevented escapes — whether by fatal shots or by someone surrendering — the soldiers got special leave. When they did military service down there at the border and got special leave, then that was incentive enough. Sometimes, practical gifts were also handed out. On the other hand: If they missed a shot, then they got the opposite of special leave. They got penal service.

Today, almost 30 years after the fall of the communist regimes, Bulgaria still finds it very difficult to come to terms with its own past. Why?

That's a very complex question because so many areas are affected. Bulgaria underwent a different transformation than Germany. Bulgaria's political elite lacked interest in coming to terms with history. For the most part it was due to the fact that many representatives of the old system remained continually active after 1990.

On the other hand, the question arises: What would have been possible at all? Where would this 100% change have come from — like it did in the GDR, where the Federal Republic of Germany was at its side and provided aid from its institutions and personnel? That was not possible in any other country.

EU accession was one of the biggest factors in the change: in the last 10 years this has improved significantly, especially when Comdos [Editor's note: "Commission for the Disclosure of Documents and Announcing Affiliation of Bulgarian Citizens with the State Security and the Intelligence Services of the Bulgarian People's Army," commonly called "Commission for Dossiers" (Comdos) in Bulgarian] began its work in Sofia.