This is ugly and unfortunate. Here's a link to LA County ordinances: http://ordlink.com/codes/lacounty/index.htm
I know it's not what you specifically asked for; although, if you don't have it, it may come in handy down the road.
Well, as the cats were dumped in a park, what about calling the parks department to inquire who to call about illegally dumped animals? We live near a cemetery and encounter a lot of dumped animals; so, I can somewhat relate to the anger, sadness, and frustration I imagine you must be feeling over this incredibly insensitve act. I do, however, have some other thoughts here as well.
First, you didn't see it happen...this doesn't mean it didn't happen, although it establishes the fact that you heard it second-hand and wish to lodge a complaint without first-hand knowledge. This won't strengthen your complaint.
Second, where are the cats now? Do you or your friend have them? If not, you lack key evidence. Unfortunately, this doesn't help either.
Third, where in Los Angeles County were the cats dumped? I used to live there and it's a pretty big place.
Lodging a complaint without first-hand knowledge or evidence doesn't present a compelling case - the person who set them free could easily claim they escaped or simply gave them away.
There's a lot of cats in Los Angeles County; unless an animal control officer captures them and draws the connection back to the owner who dumped them (e.g., tag, microchip, tattoo), I can't imagine how they'll enforce the law in this situation. And, since the person dumped them illegally, I imagine the former owner removed any and all identification.
I'm all for reporting if you have compelling evidence to support your official complaint.
A problem here (not you but in general) is that people often abuse systems that allow such reporting; so, when someone like you wants to do the right thing, it's hard to weed through bogus complaints without irrefutable evidence.
Is there any chance of educating your friend's work supervisor about this level of conduct? I surely hope the cats are altered.
Good luck here, those poor cats will need it.
I noted LesH provides a wonderful URL including the exact penal code (excellent!) and catlover_2004 very conveniently lists several terrific hyperlinked search engines - how kind and incredibly helpful!! It seems you have many people rooting for you to help these unfortunate abandoned cats.