The City of Oakland disclosed the Attack on February the 10th
The breach began on February the 8th.
On February the 14th, the the city of Oakland declared a local state of emergency due to the effect of the ransomware attack.
Play ransomware gang claims responsibility for the breach.
On March the 3rd, it was confirmed by the city that an unauthorized third party had obtained files from their system and were to be released unless actions were taken.
After this, the gang started leaking part of the dump. The first part is a 10 GB compressed file. According to information made public by the Play ransomware gang, the compressed file includes the following:
Private and Personal confidential data.
Employee full info.
Human rights violation information
Furthermore, they have indicated that if there is no reaction to this, they will upload the full dump of what they have manage to acquire.
You can read the information posted by the City of Oakland here.