Karen Read is on trial for the murder of her boyfriend, Boston police officer John O'Keefe, who was found unresponsive outside a friend's home on a snowy morning, with the case continuing to make national headlines.

Who is Karen Read and what is she accused of doing to her boyfriend, a Boston police officer? Here's a summary of her case and why it ended in a mistrial.

Dateline Producer Sue Simpson describes the frenzied atmosphere at the Karen Read trial from a journalist's perspective.

I didn’t know what the hell happened. How did the night end up like this?” Read says in a preview clip. “I felt like I was living in a nightmare.”