What I've come up with as the reason for the visit is that there's been a jury-tampering case in Pasadena and the character's name has been mysteriously removed from a couple of lists of eligible jurors (There's an explanation for this - someone else rigging the system to keep the character from getting tied up in long trials, not related to the other jury-tampering - but it isn't important).
What I need is a plausible reason for an LAPD officer to be working in Pasadena and assigned to this case. I don't want the police officer to transfer to the Pasadena police department permanently - it isn't incredibly important, but it would be against the canon of this particular character. My original explanation for this was that the Pasadena PD wanted the jury-tampering investigated by outsiders who were not involved in any of the relevant trials, but that feels a bit weak. Another possibility is that the police officer is assigned to a task force investigating similar jury tampering in Los Angeles, Pasedena, and other cities in the area, but it feels like that would be the US Department of Justice, not local police departments.
Can anyone suggest a better reason?
Searches I've tried so far:
pasadena police officer working for LAPD
lateral officer pasadena
LAPD and Pasadena PD cooperation
later - it looks like this one isn't going to work - I think I'll have them meet on neutral ground instead. Thanks to everyone who commented.