In That Sleep of Death - Adam Lapid Mysteries, #8

Not even murder can keep this secret buried. Israel, 1952 - A man lies dead in a city park, his head bashed in. No witnesses. No clues. It seems like an impossible case. The police have given up. But private investigator Adam Lapid is determined to catch the killer. Hired to investigate the murder, Adam begins digging into the victim's life. He learns the dead man was a Holocaust survivor, and that he may have had knowledge of a terrible crime that happened in pre-WWII Poland.
A crime that is still claiming victims in Israel more than a decade later. To solve the mystery, Adam must use all his wits and courage. And he must work quickly. Because the killer is already hunting for the next victim.