Is the Killer at This Party?

This has made people speculate was the perpetrator of this crime at this party and calling 911 to see how fast somebody would respond. Is it possible that one of them just picked up the phone and dialed 911 and then never confessed to it because they didn't want to get in trouble? The other thing I question though too, Captain, is what kind of staff was working this party? Would we have had people helping out whether it be caterers or somebody answering the door, valuing cars? So it could extend beyond the guest list for whoever called 911.