Plot hole: At the end of the episode McCoy and his team tape a conversation between Melissa Corbin and her mother Lorraine in order to record her admitting to murdering Alan, her first husband. Trouble is, she says nothing incriminating. The closest they get is Lorraine asking her why she killed Alan, and she replies "You didn't have to sleep with him." That means nothing, and in fact Lorraine says absolutely nothing of any legal significance during the entire conversation.
Character mistake: In the scene where Serena Southerlyn is speaking to a fingerprint expert, he tells her that he found seven false positives out of the 20 prints tested. Serena replies, "That's almost a third." It's not almost 1/3; it's more than 1/3.
The Collar - S12-E11
Visible crew/equipment: While the DAs are talking about their options in the case, after they first talk to the Priest and he refuses to testify, there is a few close ups of Nora's face. In most of these close ups the reflection of set lights are visible in her glasses.
Factual error: When Green is going over the victims' phone records, he mentions a call to the 508 area code, which they said would have been a call to his parents. The victim's parents lived in Amherst Massachusetts, which is the 413 area code.
Answer: A courtroom trial that has been terminated prior to its normal conclusion. A mistrial has no legal effect and is considered an invalid or nugatory trial. This often happens when there is a lack of Jurisdiction, an incorrect jury selection or, as seen in many of the episodes, a hung jury, i.e. some jury members finding the defendant guilty while the other members of the jury will find the defendant not guilty and all jury members won't change their decision.