Donald Lang, nicknamed "the Dummy" by Chicago cops, spends his days at the Illinois State Psychiatric Institute staring through a wire-reinforced window. In the distance he can see the sprawling South Water Street produce market where he once worked and the South Side ghetto where he grew up. A deaf-mute since birth with no language beyond a sometimes eloquent but more often incomprehensible mime, Lang has spent the last 11 of his 32 years in state institutions. His public defender describes him as a "prisoner locked in his own head." That may be changing. One recent morning Lang walked away from the window, broke into a wide smile and began animatedly "talking" with his hands about the huge trucks he used to load at the market. "He's learning sign language faster than anyone I've ever taught," declares his instructor, Candy Haight. But Lang's victory over his handicaps may well be Pyrrhic. Once he becomes fluent with signs, Lang will face trial for murder—the final reckoning of a criminal case that one judge calls "unique in the annals of Anglo-Saxon law."

The bizarre saga began in 1965, when Lang was accused of killing a well-known prostitute on Chicago's skid row. Declared unable to stand trial because of his handicaps, he spent five years in various state facilities before his lawyer argued successfully for a trial. By then the state's largely circumstantial case had evaporated with the death of a crucial witness, and Lang was freed. Six months later he was charged with killing another prostitute. This time he was tried and convicted. But an appeals court reversed the conviction, ruling that his inability to defend himself or to comprehend what was happening in the courtroom meant he could not constitutionally be tried for the crime. That left Lang in a legal conundrum: he could not be tried, but neither could the state simply let him go free.

Then last year Lang's defense team moved to have their client either declared mentally incompetent and committed legally or released. State psychiatrists called Lang "aggressive...irritable...dangerous," with the functional intelligence of a 7-year-old. But Dr. Robert Donaghue, a psychologist who is also deaf, said Lang was "of at least average intelligence and possibly bright." Cook County Judge Joseph Schneider's order: try to teach Lang sign language. "There can be no more unique 'experiment in nature' than is presented by those born deaf," he said. "They are living reminders of the state of man in prehistory, before language was evolved."

Lang's progress in the months since then has been remarkable. He can sign sentences ("I love you," "I want you telephone brother") and some 200 words. Teacher Candy Haight, though pleased with the success of the weekly three-hour lessons, senses Lang's uncertainty over his future. "I can't believe he is a murderer," she says, "but I can't ask him about it yet. What if I accidentally gave him the wrong words—if somehow by my questioning I 'programmed' him?" She remembers a day last January when he brought to his lesson some magazine drawings of Gary Gilmore's execution. "He was asking me if this would happen to him," she says. "What could I tell him? I don't know, but he's so scared."

Experts say Lang may not know enough sign language to understand courtoom procedures for another two or three years—if ever. "There's never been a case studied when they've tried to start teaching language at age 32. Maybe the circuits in his brain just go a different way now," says public defender Nancy Joslyn. Prosecutors are already pushing for a new trial, however, and when Lang took the stand for the first time last month it finally seemed a real possibility. During a hearing on whether he might be able to await trial in a halfway house rather than the asylum, Judge Schneider asked the defendant what he would prefer. Haltingly, Lang signed: "Want I go home."