It isn't the easiest of tasks to identify someone with autism in Lee's work. To Kill A Mockingbird was written at a time when the depiction of mental conditions in literature was challenging and often not appropriated in texts. The reality is that in trying to find an "idiot savant" or someone with autism is based on finding elements within the text that match how someone with such a condition could be seen.
Boo Radley would be someone that might fit the qualifications of a savant or someone with autism. Initially, Radley himself is described as someone misunderstood and misread. The construction of an imposed narrative could be reflective of someone with autism or considered to be a savant. In Maycomb, those who were like this would be seen as "different" or as the proverbial outsider, evidenced in Jem's description:
Jem gave a reasonable description of Boo: Boo was about six-and-a-half feet tall, judging from his tracks; he dined on raw squirrels and any cats he could catch, that's why his hands were bloodstained—if you ate an animal raw, you could never wash the blood off. There was a long jagged scar that ran across his face; what teeth he had were yellow and rotten; his eyes popped, and he drooled most of the time.
The manner in which Boo is described is reflective of how a traditionalist social order like Maycomb would perceive someone who is an idiot savant. Eating "raw squirrels," with "teeth... yellow and rotten," and "eyes popped" along with the detail of drool are reflective of how those with special needs would have been seen in Maycomb. Radley lives in a world "alien to Maycomb’s ways” and the question of institutionalization happens after Boo strikes his father with scissors. The aspect of social stigma against Radley is integral to his characterization and reflects how he might be someone considered to be autistic.
At the same time, Boo Radley can be seen as a savant because of his distinctive view of the world. Radley possesses the insight that compels him not to be a part of Maycomb's world. He lives in his own world, one in which its inward nature is able to appropriate Jem and Scout in it. Lee constructs Radley's character as one who possesses the insight to understand the true horror of the world: "Scout, I think I'm beginning to understand something. I think I'm beginning to understand why Boo Radley's stayed shut up in the house all this time... it's because he wants to stay inside." This insight might be where Radley could be considered to be a savant, someone whose ability to understand a particular aspect of reality that others fail to grasp. Boo's condition prevents him from being fully understood by the world around him. At the same time, he has a distinctive ability to read what others fail to understand. Both of these realities can help one to consider Boo as an example of an autistic or idiot savant type of character in To Kill a Mockingbird.