When best-selling Viennese author — and convicted murderer — Jack Unterweger was released from prison in 1990, the 40-year-old posed for the pages of a local paper, ''wearing a silk, double-breasted glen plaid shirt on top of a snow-white shirt.... He held his hand to his chin, displaying his gold rings and bracelet.'' He soon began killing again, embarking on a gruesome spree in Austria — and California. In fact, it was the L.A. police who provided the evidence that finally cracked the continent-spanning case. Though John Leake's account takes one heart-stopping turn after another, Entering Hades never crosses the line into sensationalism. A-