Certain incidents will be handled on K4 for security reasons. This was one of them.
It's not unusual to hear units dispatched to calls on K4. They don't show up on the incident page, so you have to be listening to A1/K1 to catch them. Usually, they're for standbys when PD executes an arrest/search warrant. You might hear E25 dispatched to a call on K4, and the address given will be their own station. Other times, you'll only hear the dispatch tone, and, "K-deck 4, check MDC for info", but you won't even hear what apparatus are being dispatched. Details of the call will be on their MDT, so the public can't chase it.
Other times, if there's a VIP in town, FD standbys will be on K4.
John
Peoria