It looked like Carl Lemon would be going back to jail for the 20th time. Saddled with a 25-year record of shoplifting, drug dealing, and assorted other crimes, not to mention eight aliases, Lemon had made it easy for prosecutors. He even signed a confession saying that he had stolen a woman’s purse while she ate in a Back Bay restaurant. A second victim, whose bag he also snatched, had driven overnight from Canada to testify against him. But, as the two victims watched in disbelief, the judge set Lemon free, saying that the career criminal, then 43, needed a detox program, not jail time. When the detective who arrested Lemon rolled his eyes and muttered that the decision was a disgrace, Judge Raymond G. Dougan Jr. had court officers lock him up for the morning instead.