Following a 15-month investigation, Cal Fire investigators said Thursday the deadly October 2017 Tubbs Fire was caused by a private electrical system next to a residential structure.

The findings clear California's Pacific Gas and Electric utility of any blame for the fire.

In a recent court filing, PG&E blamed unpermitted work by a caretaker on privately owned electrical equipment at a property outside Calistoga for sparking the Tubbs Fire.

"The evidence supports the conclusion that this equipment, located beyond PG&E’s service delivery point, was planned, designed, installed, maintained and operated by third parties, not PG&E,” the company said in the filing.

The caretaker lacked electrical training and said he did not obtain permits when he replaced a pole on the property that helped to provide power to a well and other structures in 2017, the company claimed in a filing before federal judge William Alsup.

While the company does not say exactly what went wrong or if the replaced pole was specifically to blame, it did say "when PG&E examined evidence at the incident location following the Tubbs Fire, PG&E observed that one of the customer-owned poles was severely burned at the top."

PG&E says the property on Bennett Lane in Calistoga was owned by Ann Zink. The caretaker, Michael Andrews, said he was driving up the driveway of the property in early 2017 when he noticed that one of the poles had broken and the line was dangling three and a half feet above the driveway. He says he used a rope to snag the lines and pull them away and then kept them up by a stake. He later enlisted a third party to help him put in a replacement pole, but did not get permits.

The company did admit that due to a “mapping error,” vegetation around one of its nearby poles was not properly cleared, but said the problem was south of the Zink home and the damaged equipment at her home.

In the Cal Fire report, investigators were not able to pinpoint what triggered the fire on the Bennett Lane property, however, saying that the fire itself inflicted severe damage to critical potential evidence. But they were able to rule out PG&E’s equipment as responsible.

PG&E released the following statement Thursday afternoon following Cal Fire's announcement:

"Without question, the loss of life, homes and businesses during these devastating wildfires is heartbreaking, and we remain focused on helping affected communities recover and rebuild. The safety of our customers and the communities we serve is our most important responsibility, and we are committed to assessing our infrastructure to further enhance safety and help protect all of the customers we serve from the ever-increasing threat of wildfires."

PG&E announced earlier this month to file for Chapter 11 bankruptcy protection because of its liabilities from devastating wildfires in Northern California.

Investigators did not identify any violations of state law or Public Resources Code related to the cause of this fire, according to a statement sent out by Cal Fire.

The Tubbs Fire in Sonoma County started on the evening of Oct. 8, 2017, and burned a total of 36,807 acres, destroying 5,636 structures and resulting in 22 deaths. One firefighter was injured in the fire.

In total, the Tubbs Fire involved more than 170 fires and burned at least 245,000 acres in Northern California. Approximately 11,000 firefighters from 17 states as well as Australia helped to get the fire under control.

According to CNBC, PG&E shares resumed, and sharply spiked 77 percent after California investigators cleared the utility of blame for the 2017 fire.

In a statement, the City of Santa Rosa said they will be reviewing Cal Fire's findings with their legal team.

In their statement, Cal Fire added that "Californians must remain vigilant and take on the responsibility to be prepared for wildfire at any time throughout the year.

For more information on how to be prepared, visit www.readyforwildfire.org or www.fire.ca.gov.

PG&E's full statement on Cal Fire's investigation:

"Without question, the loss of life, homes and businesses during these devastating wildfires is heartbreaking, and we remain focused on helping affected communities recover and rebuild. The safety of our customers and the communities we serve is our most important responsibility, and we are committed to assessing our infrastructure to further enhance safety and help protect all of the customers we serve from the ever-increasing threat of wildfires."

Cal Fire has completed its investigation of the 2017 Tubbs Fire and concluded that PG&E facilities did not cause the fire.

The devastating and unprecedented wildfires of 2017 and 2018 have had a profound impact on our customers, employees and communities. Regardless of today’s announcement, PG&E still faces extensive litigation, significant potential liabilities and a deteriorating financial situation, which was further impaired by the recent credit agency downgrades to below investment grade. Resolving the legal liabilities and financial challenges stemming from the 2017 and 2018 wildfires will be enormously complex and will require us to address multiple stakeholder interests, including thousands of wildfire victims and others who have already made claims and likely thousands of others we expect to make claims."