Police were called to the tragic birthday party in Berkeley less than an hour before the balcony crashed - but did not go because of a reported shooting elsewhere in the city.
A neighbour made a complaint about the noise from the fourth floor apartment at Library Gardens at 12.02am local time - eight hours behind UK and Ireland time.
But police chief Mike Meehan said they never attended because four minutes later they were called to the scene of reported gunfire in south Berkeley. This reported incident was obviously prioritised, he said.
Once the balcony was reported collapsed, shortly after 12.40, officers were on the scene within two minutes.
The police chief said there is no evidence of foul play or criminality at this stage of their inquiries.
Berkeley City mayor Tom Bates vowed "not to leave any rock unturned" in investigating the causes of the collapse.
He said it was a wake up call at a time when many other buildings were under construction in the city.
The property management company said the owner was an entity called Blackrock.
Inspection histories as well as other records on the building are being reviewed.
Authorities have vowed to make the records public.