Which character is most psychologically flat in Trifles by Susan Glaspell?

In Trifles, George Henderson, the County Attorney, is the most psychologically flat.

As such a flat character, Henderson remains the same throughout the story, "Trifles." For, all the way to the end of the narrative, he retains his original attitude that the things with which women occupy themselves are insignificant and mere "trifles." He also cuts off Mr. Hale when this neighbor of the Wrights tries to relate what he has said to Harry about...

In Trifles, George Henderson, the County Attorney, is the most psychologically flat.

As such a flat character, Henderson remains the same throughout the story, "Trifles." For, all the way to the end of the narrative, he retains his original attitude that the things with which women occupy themselves are insignificant and mere "trifles." He also cuts off Mr. Hale when this neighbor of the Wrights tries to relate what he has said to Harry about not knowing "as what his wife wanted made much difference to John Wright," a statement which could lead Henderson to find a motive.

Because of Henderson's arrogant dismissal of anything that might be found in the kitchen of the Wrights' house (he gives only a cursory look in one cupboard), and because he does not listen carefully to things that may at first seem insignificant, he misses the incriminating evidence for which he and the other men have searched everywhere else in the house. 

Ironically, it is the evidence discovered in the kitchen--the place of mere "trifles,"--that could have brought him a conviction of Mrs. Minnie Wright, who is being held in the jail and due to go on trial. Furthermore, Mrs. Hale and Mrs. Peters hide the evidence from Henderson and the sheriff partly because of the men's dismissal of the "little things" in which only women are interested and because of Henderson's sarcasm when Mrs. Hale mentions that the Wright home was not cheerful:

No--it's not cheerful. I shouldn't say she had the homemaking instinct.

Also because of his flippancy, Henderson misses the significance of Mrs. Hale's pondering about the quilt she has been sewing that they discover, "I wonder is she was goin' to quilt it or just knot it?" For, this is a question whose answer could be a clue. Instead, he jokes, "Well, ...at least we found out that she was not going to quilt it. She was going to--what is it you call it ladies?"