In Trifles, it was Minnie Wright who killed John Wright. In the play, Mr. Hale describes how Minnie acted the day he discovered that John was dead.
According to Mr. Hale, Minnie seemed agitated when he questioned her about John. Mr. Hale related that, when he entered the Wright residence, Minnie was rocking back and forth on her chair. She had her apron in her lap and appeared to be pleating it. Minnie was in an odd mood; she was nervous and obviously troubled about something.
When Mr. Hale mentioned the cold weather, Minnie barely acknowledged him. She indulged in no pleasantries whatsoever and refused to look at Mr. Hale. When Mr. Hale asked to see John, Minnie gave a strange little laugh. Since she gave no real answer, Mr. Hale was forced to ask again. After much prodding on Mr. Hale's part, Minnie finally admitted that John was dead.
She pointed upstairs and revealed that John died "of a rope round his neck." Mr. Hale then went upstairs to investigate. After finding John dead, he went back downstairs to ask whether anyone had been notified of John's death. Mr. Hale relates that Minnie answered in the negative and appeared to be unconcerned. When Mr. Hale asked who was responsible for John's death, Minnie maintained that she didn't know. She mentioned that she was a sound sleeper.
Minnie's odd behavior, detached answers, and nervous laughter show that she was obviously in shock. It is plain from her emotional angst and the women's conversation about the dead canary that Minnie was responsible for John's death.