Investigators have concluded that arson was definitely the cause of the fire that destroyed the roof and second floor of the Walgreens building in downtown Palo Alto the night of July 1-2.
The fire caused about $8 million of damage to the building, constructed in 1900, investigators estimate -- up from an earlier estimate of $5 million to $7 million and an initial guesstimate of $3 million to $5 million.
A week-long investigation, including talking to witnesses, concluded that arson was definitely the cause of the fire because of evidence found at the scene, police Sgt. Sandra Brown said.
Investigators are not saying where the evidence was found.
"We don't want to talk about how we determined it because we are still looking for a suspect," Brown said.
Palo Alto police and fire investigators were assisted by the Santa Clara County Arson Investigation Task Force and investigators from the federal Alcohol, Tobacco and Firearms agency.
Fire Chief Nick Marinaro said last week that arson had been suspected because flames were already shooting out of the roof when the first engine arrived.
The fire at the Walgreens building at the corner of University Avenue and Bryant Street was first reported at 9:30 p.m. Sunday, July 1. It eventually went to four alarms with more than 50 firefighters from Palo Alto, Menlo Park, Mountain View, Santa Clara County and Santa Clara trying to put it out.
The fire burned most of the night and frustrated firefighters who couldn't pour water directly onto the flames until part of the roof collapsed.
The collapse of the roof delayed the ability of arson inspectors to get into the building until last Friday because the roof had given support to the walls, which became unstable.
The building was temporarily shored up, allowing arson investigators to enter it.
The danger of the building's total collapse has kept University Avenue and Bryant Street closed to both vehicular and pedestrian traffic in the immediate vicinity.
The building may not be able to be repaired, a building contractor told the city last week. If that is the case, the city would want the building demolished as soon as possible so that University Avenue and Bryant Street can be reopened to traffic again, city officials have said.
Officials will now begin to determine what will happen to the now-structurally unsound building, Brown said. Zoning restrictions in the area would most likely restrict any replacement structure to approximately the same size as the existing building, according to city planning officials.