Arson probers said the fire started from the legislative section of Room 603 at around 6:40 a.m.
Fire Inspector Leon Andiso said damage was estimated at half a million pesos. Among the items destroyed or damaged were several computer units and various documents.
He said the fire at the 30 square-meter section of the office was declared out at exactly 8:10 a.m.
As of press time, Andiso said they were still waiting for the result of the crime laboratory examination of debris before the actual cause of fire could be determined.
"We are looking at several possibilities," Andiso said in an interview. "The fire could have started from short-circuit involving an unattended handheld radio charger."
However, the fire investigator said they are not discounting the possibility that somebody deliberately set fire to the room.
"There is a 10 percent possibility of an arson case," he said.
Andiso said the members of the senator’s staff were sure that they locked the office when they left it last Friday night.
"The security guard on duty also confirmed that nobody entered the office before the fire," he pointed out.
Andiso said they had to be extra careful in putting the fire out, noting that security officers of the Senate even regulated their response.
"They limited the number of firefighters inside the building," he said. "They were worried that too much water might affect the offices of other senators. Luckily, the fire was manageable even with minimal water."
Meanwhile, Michelle Villasenor, secretary general of the VP Loren Movement, raised suspicion that the fire was the work of saboteurs as she noted the "increasing intensity and desperate nature of the covert and overt attacks against Loren."
"I’m not pinning the blame on anyone, but investigators should seriously consider attempted arson as the cause of this fire that was luckily immediately put out by alert Senate personnel and firemen," she said.