Answer:
Birds are innocent and harmless, like Tom and Boo
Explanation:
Atticus, a prominent and wise lawyers tells his children that it´s a sin to kill a mockingbird because they are innocent & harmless.
Tom symbolizes innocence: he is wrongly accused of raping a white woman.
Arthur ¨Boo¨¨ Radley is a harmless character, but unfortunaly he has to deal with a group of children under the spell of prejudice and superstition.
In medias res means to start a writing with events that happened in the middle of the story, then continuing the story from the beginning.