Firefighters say it was a Molotov cocktail, or something like it, was thrown through the window scorching the inside of the records room.
"We had flames coming out two sections of windows on the first floor," said acting fire Capt. Cliff Campbell.
Campbell's Engine 21 was the first to arrive; he called for more help, but for several minutes he and his crew were the only ones there for roughly four to five minutes.
Those minutes are critical because had the arsonist waited a week, Engine 21 would not have been just a mile away. Budget cuts in the bankrupt city are forcing the department to move Engine 21 starting Monday.
"Another four or five minutes at the rate it was burning, would've been a devastating fire for the county," said Bill Tweedy from the Vallejo Fire Department.
Tweedy is a lead investigator on the fire and says the department is reviewing security tapes and focusing on finding the arsonist. But for the courthouse facilities manager, the fact that Engine 21 is getting moved out of the neighborhood comes as an unhappy surprise.
"That would be sad because if they were the first to be here today, their role was crucial in getting this fire under control," said court facilities manager Sabra Forbes.
The records at the courthouse cover civil and criminal cases. Fire investigators believe someone involved in a case wanted records destroyed.
Yvonne Lafferty came to court to file records in a landlord-tenant dispute.
"You'd think your records would be safe in the court house but..." said Lafferty.
She and others were told to come back on Friday. For Engine 21, the number of tomorrows in this neighborhood is dwindling down to the end of this week. Neighbors are upset.
"What can we do about it? We can't do nothing. These stupid people who run Vallejo..." said one angry neighbor.
Campbell says the firehouse may get another crew as trucks and engines are shuffled around.
"This is a higher call volume station so they're looking at ways to try and bring another unit over here, but what that'll result in is a station closure somewhere else," said Campbell.
There is no getting around the fact that Vallejo used to have eight engines and after Monday, the city will have four.
Anyone with any information about this case is asked to contact the Solano County Sheriff's Office at 1 (707) 421-7090 or Crimestoppers at 1 (707) 644-STOP.
For anyone with business at the courthouse you can call 1 (707) 702-7475 after 10 a.m. to find out more about rescheduling.
The courthouse will be closed on Thursday and there is a 50/50 chance it'll open on Friday.