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Petaluma Police Department
Wednesday January 1st, 2020 :: 12:26 p.m. PST


Petaluma man arrested for Attempted Murder and Unlawful Possession of a Firearm.


Petaluma Police Department

For Immediate Release                                                                                                                                                                     Wednesday, January 1, 2020
Issued By:
Detective Sergeant Paul Gilman, Petaluma PD, 707.778.4415, email:
Incident:                     Arrest for Attempted Murder/ Unlawful Possession of a Firearm
Report Number:         19- 5411
Occurred Date:          December 31, 2019
Occurred Time:          5:06 PM
Location:                    101 Ellis Street
Suspect(s):                 William P. Hanson, 70-year-old Petaluma resident
Victim:                       Barry Costa, 61-year-old Petaluma resident
Incident Summary
On 12/31/2019, Petaluma PD Dispatch received 911 reports of a fight between 2 males. During the altercation, one male produced a firearm and fired it at the other. Officers arrived on scene and located a male laying in the parking lot of the Town House complex with what appeared to be 2 injuries consistent with gun shots. The other male was detained by bystanders.
During the investigation it was determined that Hanson had been acting erratically in the parking lot area. Costa walked into the parking lot and a verbal altercation ensued. The verbal argument turned into mutual physical combat and during that physical fight, Hanson produced a .22 caliber Derringer revolver and fired a single bullet into Costa.
Costa was taken by ambulance to Santa Rosa Memorial Hospital. Hanson was arrested and transported to Petaluma PD. After evidence was collected from Hanson, he was transported to Petaluma Valley Hospital for medical attention and medical clearance to go to Sonoma County Jail. Hanson was booked for Attempted Murder and Unlawful Possession of a Firearm.
A search warrant was sought and obtained for the room Hanson was renting and his vehicle.
Anyone with information regarding this case is encouraged to contact Petaluma Police Detective Ryan McGreevy at (707) 778-4334. For media inquires please Detective Sergeant Paul Gilman at (707) 778-4415.

Petaluma Police Department
969 Petaluma Blvd N
Petaluma, CA 94952

Emergency: 9-1-1
Non-emergencies: 707-778-4372

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