Closed an occupied REO but can't find out who lives there

[Sam Liu]

I just closed an occupied REO SFH in California last week. I drove by the house but it seemed no one lived there. From the windows, I saw there was a big mess inside the house: very dirty carpet; old and dirty furniture randomly stacked on each other; all kitchen cabinet drawers were pulled out; no clothes, dishes or food, no any sign that someone lives there. But there is a dog inside barking and a lot of dog pops on the dirty carpet. It's a mess!

So I talked to the neighbors. They said owner didn't live there and they saw some people with kids who claimed as tenants, but they haven't seen these people for a couple of weeks. An old lady was worried that the dog was abandoned, so helped monitor if anyone came in to feed the dog. Two days later, she told me there was a guy came at night and left. It seemed he went to feed the dog but didn't live there (I can't imagine if anyone can live in there). 

I served a notice, said I'm the new owner and asked them to contact me if they are tenants. No one contacted me so far. It's such a confusing and weird situation. I originally planned to meet either previous owner or tenants to discuss cash-for-key or agree on something. But now I even can't find out who lives there (tenants or just squatters?) If they are tenants, they would call me, right?

Looking for help here to handle this situation.Are these people just use the house for their junk and pet? If that's case, can I consider this house is abandoned? If still no one calls me, I'll ask animal control to remove the dog and gain the possession? Or I need to do 90 days notice to start eviction assuming tenants still live there? (Gosh, just found out CA requires 90-day notice now). But the house is really in a bad condition. Can I do 3-day eviction notice because they didn't maintain the house properly?