How would one go about collected a reward for giving a tip that leads to an arrest?

A couple years ago there was a homicide in my city. Today, the family of the victim placed a $30,000 reward for any information that leads to an arrest of the suspects that are responsible for the homicide. The local police posted this reward on their Facebook page. Is the family legally obligated to pay out the reward if i give information that leads to an arrest? How would I go about ensuring that I receive that reward