Berlin, July 20, 1944: Colonel Claus Schenk Graf von Stauffenberg headed to Adolf Hitler's Wolf's Lair field headquarters. It was still early, just before 8 a.m., on the day Stauffenberg planned to kill Adolf Hitler with a bomb. It was too good an opportunity to miss: Stauffenberg was supposed to brief Hitler as part of his military duties.

Kurt Salterberg, now 91, was a guard at the Wolf's Lair, near what was then Rastenburg in East Prussia and today is the Polish town of Ketrzyn, some 600 kilometers (370 miles) east of Berlin. Back then, 21-year-old Salterberg was part of the team protecting the inner area.

At around 11 a.m. Stauffenberg and two co-conspirators, Major General Helmuth Stieff and First Lieutenant Werner von Haeften, entered the command headquarters of the Nazi regime. It was where the most powerful military figures would meet and where Hitler would hand out orders to his officers.

Even today, Salterberg is still able to recall the smallest details. "Everything was blocked off. I had to check every single person who wanted to meet Hitler," he said.

Field Marshall Wilhelm Keitel brought along a group - Salterberg let them pass through since Keitel had an identification card. "That's why I didn't have to check his companions."

'Nothing out of the ordinary'

Stauffenberg was also among the people Keitel brought in. "I noticed him right away because of his war injury - he was wearing an eye patch," Salterberg said. "Stauffenberg was carrying a briefcase, but there was nothing out of the ordinary."

11:30 a.m.: Stauffenberg retreated to one of Keitel's barracks to go through possible questions Hitler might have in the meeting. Stauffenberg had two packages of explosive agents on him, said Johannes Tuchel, head of the German Resistance Memorial Center in Berlin.

"Stauffenberg excused himself under the pretext that he had to freshen up and left the room. He then went next door to arm the package of the explosives with the help of Haeften." Crucially, they only planted one of the packages of explosives in the briefcase.

12:37 p.m.: Keitel introduced Stauffenberg to Hitler. Unnoticed, Stauffenberg then put the briefcase with the explosives under a map table next to Hitler. Shortly before it was set to explode, Stauffenberg excused himself, saying he needed to make a phone call. It was now 12:40 p.m.

Salterberg said he noticed that Stauffenberg left the briefing after a short period of time. But it was nothing out of the ordinary. "That did happen sometimes, when someone wanted to quickly go get documents."

Chance came to Hitler's rescue

It was now just two minutes before the detonation. Colonel Heinz Brand unsuspectingly moved Stauffenberg's briefcase to the opposite end of the table. This action would lead to his own death - but would spare Hitler.

Shortly after, the bomb went off that Stauffenberg had left behind. "Paper was floating through the air, there was wood and splinters, a massive cloud of smoke," Salterberg said. "One of the men present in the room was hurled through the window, others came flying through the door. It was absolute chaos!"

Panic spread quickly through the headquarters. No one knew what had just happened. "People cried out for help, rolling on the floor," Salterberg said.

At first it was unclear whether Hitler had survived the assassination attempt. "Everyone was shouting: 'Where's the Führer?' And then Hitler got out of the building, supported by two men," Salterberg recalled.

1 p.m.: Stauffenberg was convinced Hitler was dead. He and Haeften left the Nazi headquarters. They planned to get to Berlin as quickly as possible to organize the toppling of the entire Nazi regime. They already had a plane waiting for them.

But their assassination plot failed. The meeting with Hitler was moved to a wooden building instead of the usual bunker. If it had been a solid bunker with concrete walls, or the case had not been moved, or if both explosives had been used, "Hitler would have been killed in the attack for sure," Tuchel said.

World has been turned upside down

After the failed assassination attempt, the Nazi regime took vengeance on the "traitors" and their families. Gestapo secret police arrested Stauffenberg's wife Nina and took away their children. They were put in an orphanage in Bad Sachsa in the Harz region of central Germany.

Stauffenberg's 10-year-old son Berthold and his three younger siblings were among the children placed in the home. "It was awful, of course, since we were separated from our family and we didn't know anything. We were alone," Berthold Maria Schenk Graf von Stauffenberg said. He was born in 1934 in Bamberg.

"We were raised like all the other kids in our class. That means, to some extent, we were little Nazis as well," he said. "My mother didn't push for it, but she also didn't speak up against it - for good reason, because it would have cast suspicion on her and my father."

Stauffenberg speaks in a relaxed manner, using only few gestures. On July 20, 1944, however, his world turned upside down. "I heard about the assassination on the radio, but they weren't giving any names. The next day, my mother told me that it was our father. That was a shock and very confusing: How could he attack the Führer? But I know one thing for sure: I never thought of him as a criminal."

'Traitors' sentenced to death

The regime then put on its notorious show trials at the so-called People's Court in Berlin. Judge Roland Freisler presided at the trials, and it was clear from the start that he had already signed the death warrants for the accused before the proceedings had even started.

By April 1945, 89 people had been executed in Berlin's Plötzensee prison on charges of having belonged to resistance movements or having supported it. The wives were informed of their husbands' executions in a letter and families were required to pay the cost of the trial out of their own pockets.

The younger Stauffenberg didn't know any of this at the time. His parents never spoke about politics with him or his siblings. Stauffenberg said he was not surprised that his father was leading a double life at the time: "Every conspirator does that. Back then, we even heard of kids denouncing their parents. A 10-year-old, like I was at the time, couldn't have it both ways."

In 1956, as a 17-year-old, Berthold Graf von Stauffenberg decided to enlist in the army. His mother advised him to do it, but she wasn't happy about it when he did, he recalled. When joining the German armed forces, the Bundeswehr, he met former officers who served in the Wehrmacht, as the armed forces in the Third Reich had been called. He eventually rose to the rank of major general and was Germany's longest-serving soldier when he retired in 1994.

He was always aware of the fact that he was trying to equal his father, he said. "Formally speaking, he was a traitor, but I think what he did was legitimate. I was always of the opinion that he didn't give his life for the country at the time, but he did do it for Germany."