The county attorney will be prosecuting the case against the suspect in Mr. Wright's murder. It would be difficult if not impossible to prove someone murdered him (and who that person was) without a plausible motive. Therefore, when Mr. Henderson, the attorney, enters the Wright home, along with Mr. Peters and Mr. Hale, it is of the utmost importance that he discover and analyze evidence that could point to such a motive.

Mrs. Wright, the wife of the victim, is being held in jail, but the attorney must prove she killed her husband. The male characters spend their time looking at the scene of the crime and at the home's entrances/exits, but they do not investigate some of the domestic spaces thought to be "the woman's sphere." The wives of Peters and Hale, though, look around the living room and kitchen as they gather items to bring to Mrs. Wright. They notice she has left kitchen tasks unfinished and that she has dropped a stitch in her sewing. The women use their personal experience to infer that Mrs. Wright was disturbed in what she was doing and was upset. This information could've led the attorney towards a motive, but he and the other men think that what their wives are interested in are "trifles." The women discover the bird with a broken neck in Mrs. Wright's sewing kit, and this is the strongest piece of evidence to prove motive. However, they sympathize with Mrs. Wright given her controlling marriage and their own guilt for not being better friends to her, so they keep the motive hidden. It is unlikely the attorney will be able to prosecute Mrs. Wright.

In a court of law, it is important for a prosecutor to have a motive (reason) for a defendant to commit a crime (particularly a murder).  When a prosecutor is presenting evidence, they must prove, beyond reasonable doubt, that a defendant is guilty.  Part of doing so requires showing that the defendant has a motive for committing the murder.  For example, in "Trifles," without the canary, the county attorney does not have a motive.  This is why the women ultimately decide to NOT let the men know about the canary.  Of course, this was not the ONLY motive for killing her husband (it was years of abuse), but it was the last straw for Mrs. Wright to kill her husband.