Dr Efraim Zuroff, director of the Simon Wiesenthal Center in Israel, has dedicated his life to tracking down and prosecuting those responsible for the atrocities of World War II.
Many war crimes suspects are elderly and infirm and so are the witnesses. Memories are fading, but Mr Zuroff says he will not give up, "not until the last Nazi war criminal is prosecuted."
He told HARDtalk the task of bringing Nazi criminals to justice is often frustrating but he believes it is an obligation to the victims of the Holocaust to keep trying.
You can watch the full interview on the BBC News Channel on Wednesday 17th February 2010 at 04.30 and 23.30 GMT.
And on BBC World News at 04:30, 09:30, 15:30, 21:30 GMT.