Given the task definition and input, reply with output. In this task, you will use your knowledge about language (and common sense) to determine what element the marked number refers to. The numbers are marked with two underlines around them, like: _ number _. Your answer should be chosen from the given text, and should not contain other words.

Megan Hunt: I 've had other missing person cases before . Why this _ one _ ?
Kate Murphy: I was new here . It was my ... it was my third autopsy : a battered mom , whose daughter gone missing . Curtis and I worked on that case for two weeks straight
Megan Hunt: They never found the girl ?
Kate Murphy: They found her . She was my fourth autopsy .
cases