Arson cases on Oahu are on the rise.
The Honolulu Fire Department said 12.9 percent of residential fires were intentionally set last year, up from 7.4 percent in 2011.
Firefighters and the Honolulu Police Department are asking the public to keep their eyes and ears open.
"Anyone who witnesses suspicious activities such as persons fleeing the scene of a fire should contact the police and provide physical descriptions and vehicle descriptions if possible," said Honolulu Police Department Captain Richard Schaab.
Honolulu Fire Department Battalion Chief Socrates Bratakos said, "If you think that there is something fishy, that this might have been an intentional fire, help us when we come around and ask you questions."
Honolulu city prosecutor Keith Kaneshiro said, "Cases would not be successfully prosecuted had witnesses not come forward and gave us information."
Kaneshiro said arson is punishable by a mandatory 20 years and that it's a much more serious crime than many think.
"Property crime escalates to a crime that puts people in danger and have killed people," said Kaneshiro.
An elderly man died in a Liliha house fire in 2011 and an elderly woman was killed in a Pearl City blaze last year.
And firefighters said the danger doesn't end when the fire's out.
"Let's say that the structure is what we term a black hole, it's burned, it's damaged. It's still off gassing, what we call off gassing, said Honolulu Fire Department Captain Jeff Hooker. "There's still toxic chemicals, toxic odors that we have to protect ourselves against as investigators."
It's currently National Arson Awareness Week and this year's theme is "Reducing Residential Arson."