The defense team's primary argument for their clients' innocence in the Dec. 2016 Ghost Ship fire is facing its first major test. Retired Oakland fire inspector Maria Sabatini, a 30-year veteran with the OFD, testified Tuesday that the fire was most likely sparked by an appliance or other electrical source, and her team found no evidence of arson.

Sabatini said on the witness stand that this was the "most complex" fire she had ever investigated in her career, due to the number of bodies involved and the amount of debris. As KQED reports, Sabatini and her team sifted through the debris by hand seeking burn patterns and accelerants. While the investigation officially left the cause of the fire undetermined — a fact that the defense has seized on with its arson theory — Sabatini said the team did conclude that the fire began in a rear area of the Fruitvale District warehouse where there were two refrigerators and a toaster oven. She also added that three witnesses reported seeing the first flames in this area as the fire began.

Sabatini is set to be cross-examined by the defense team Wednesday, and as ABC 7 reports, a new attorney on the team, Andrew Stein, will be leading the cross-examination.

Defense attorneys Tony Serra and Curtis Briggs have said that they have witnesses who heard breaking glass and "popping" sounds associated with Molotov cocktails, and put forward an account of a half dozen Latino men who were allegedly seen leaving the building at the time the fire broke out.

Sabatini said her investigation found no evidence of broken glass that would be associated with such devices — and as the Chronicle notes, the prosecution " zeroed in on ... Sabatini’s expertise on 'fire bombs,' prompting her to give the Alameda County courtroom a tutorial on how they’re created."

Defendants Derick Almena and Max Harris stand accused of 36 counts of involuntary manslaughter. Almena, who was the leaseholder for the warehouse space that became nicknamed The Ghost Ship — in part because of its heavily built-out interior lined with recycled wood, resembling the interior of an old ship — was the person largely responsible for the interior buildout and subleases to multiple artists who lived in the space illegally. Harris was said to be Almena's second in command, sometimes collecting rent from tenants, and was serving as the doorman the night of the music event when the fire occurred.

Testimony in the trial is expected to go through July.

Previously: Judge In Ghost Ship Trial Warns Jury, Holds Closed-Door Hearing On Outside Communications