As an 18-year-old British soldier and war crimes investigator, he entered the Belsen concentration camp in Germany on the first anniversary of its liberation. The memory has remained with him.
"Ever since, I've been haunted by the grief of the survivors," he said in his opening remarks yesterday.
"There was no Israel, there was no Jewish state, there was no country that wanted them and there was no hope of justice.
"It was then that I determined that one day, somehow, I would try to do something to bring some sustenance, some hope to the survivors and their families."
Lord Janner, who is now the chairman of the Holocaust Educational Trust, was doing his national service with the Royal Artillery when he made contact with Belsen, which was the only camp for displaced Jews in the British zone of Germany.
His first visit to the camp was to a service of remembrance. "I remember every second of that day. I can remember standing by mass graves, with signs saying here lie 10,000 bodies, here lie 5,000, and a few individual graves," he said.
"Everybody was crying as they said memorial prayers. I suddenly found myself in the worst hardship and misery I could conceive."
Afterwards they took him for tea with 50 orphans, all dressed in clothes made from American army blankets.
"I remember one little girl turning her face to the wall and singing a song about crying for her mother. It just tore me apart. Then there was another little, Ella, who wouldn't talk to anybody." Lord Janner said he was so shocked and moved that for the next two years he gave all his spare time to helping in the camp.
"The whole of this conference is a dream," he said. "It's brilliant. Here are 40 nations who have come together and started to co-operate. This conference is entirely unique. It's a great international recognition of moral debt."
He said it provided new hope for an energetic quest for truth which must lead to more restitution for Holocaust survivors and their families.
"Is it not devastating that 50 years after the end of the war we still do not know the full and real truth about what happened to Nazi gold and especially individual non-monetary gold torn from people, most of whom were murdered?
"No one can ever return to the victims and their families their wrecked lives, their murdered relatives, their homes and their hope, but we can at least seek to uncover the truth."Reuse content