OAKLAND (CBS SF) – A special agent with the federal Bureau of Alcohol, Tobacco, Firearms and Explosives testified Thursday that investigators didn’t find any evidence that an explosion caused the Ghost Ship warehouse fire in Oakland in 2016 that killed 36 people.

However, ATF agent Barbara Maxwell also said she and other investigators were unable to come to a conclusion about the cause of the fire during a music party at the warehouse in the 1300 block of 31st Avenue on the night of Dec. 2, 2016, and couldn’t rule out various possible causes, such as an explosion.

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Maxwell is on the witness stand for a second day in the trial of Ghost Ship master tenant Derick Almena, 49, and creative director Max Harris, 29, who face 36 counts of involuntary manslaughter, one for each of the fire victims.

Prosecutors allege that Almena and Harris are criminally responsible for the fire because the people at the party didn’t have the time or opportunity to escape the blaze since the warehouse didn’t have important safeguards, such as fire extinguishers, smoke alarms and lighted exit signs.

Prosecutors also say Almena and Harris violated the terms of the warehouse’s lease by turning it into a living space and hosting underground music parties there.

But attorneys for Almena and Harris allege that the fire was an act of arson that they couldn’t have prevented and say they believe the blaze may have been started by a Molotov cocktail that was thrown into the warehouse.

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Maxwell testified on Thursday that investigators didn’t find any evidence, such as broken containers, consistent with a Molotov cocktail being thrown into the building.

But under cross-examination by Harris’ lawyer Curtis Briggs, Maxwell admitted that she doesn’t know where all of the remains of the fire have been preserved.

When Briggs asked, “If I want to show the jury a broken bottle and say this is how the fire started,” Maxwell conceded that she doesn’t know where he could find such possible evidence.

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