A crime historian explores groundbreaking cold-case investigations, the advent of DNA evidence, and its role in long-delayed convictions and exonerations.   When geneticist, Professor Alec Jeffreys worked with Leicestershire police on the 1986 case against Colin Pitchfork--the first person convicted of murder based on DNA evidence--a revolution started in the application of forensic expertise. Since then there have been several major cases in which long-standing murders and rapes have been revisited by teams of cold case detectives. Armed with DNA sampling, they have changed the landscape of criminal investigation, as well as the fates of those who thought they could get away with murder, and those who were wrongly convicted.   From initial and intensive DNA lab work to the final serving of justice, true crime historian Stephen Wade examines some of the most high-profile cases of recent years: the controversial suspect in the murder of Rachel Nickell in London; the unsolved slayings of schoolchildren Keith Lyon and Lesley Molseed; the notorious World's End pub killings; the erroneous charges against the "Cardiff Three"; the fate of Sean Hodgson, subject of one of the greatest miscarriages of justice in English history; and many more.