On several occasions, Boere, who is in a wheelchair and lives in a nursing home in Germany, has admitted to murdering the three, who were resistance fighters. But he said he did not do it in cold blood.
The prosecution argued that Boere voluntarily joined the SS shortly after the Nazis had overrun his native country, the Netherlands, in 1940.
He was sentenced to death in absentia at a trial in Amsterdam in 1949, but managed to spend six decades one step ahead of the law.
The Dutch authorities tried several times to have him extradited but were unsuccessful.
The slow wheels of justice have caused frustration with many, but the German judiciary system has been fairly relentless in its prosecution of Nazi perpetrators, says Edith Raim, a historian at the Institute for Contemporary History in Munich.
Boere's case was a "complicated one", she told RFI, with different legal statuses in different countries prolonging the process of prosecution.
Many people today might raise the question of why it is necessary to jail an 88-year-old man in a wheelchair, says Raim, but "it's part of Germany's moral obligation towards the victims of these crimes that these crimes are still being prosecuted."