Which detail best supports the fact that "The Catnapper" is a mystery?

Question

Cara and Wesley do not know who has taken the cats.
Cara and Wesley care about the people in their town.
Cara and Wesley talk to Mrs. Pebble as she bird-watches.
Cara and Wesley’s first impression of Barney is wrong.

Answer 1

The detail that best supports the fact that "The Catnapper" is a mystery is:

Cara and Wesley do not know who has taken the cats.

This detail directly relates to the core element of mystery, which involves an unknown element or a crime (in this case, the disappearance of the cats) that the characters need to investigate or solve.