The investigation into the fire at the San Diego Zoo is still open, Luque said. However, he added that evidence collected points to arson as the cause of the blaze. Luque declined to disclose what led investigators to that conclusion."Investigators incorporate surveillance video, employees, visitors [and] any kind of threat situations -- which I'm not saying existed in this case -- but that's how they approach the investigation," said Luque. "They approach all possibilities."No arrests had been made by mid-afternoon.Security personnel reported the fire just before 2 a.m.When firefighters arrived, The Panda Shop, located in the heart of the Zoo in a canyon, was fully engulfed.Firefighters were able to quickly extinguish the fire, but the roof of the 15-year-old gift shop caved in and the business sustained extensive damage.The fire caused about $500,000 in structural damages and consumed about $200,000 worth of merchandise and other contents, according to Luque.The fire was burning about 50 yards away from the panda exhibit and a large bird aviary, but Zoo officials said the animals were never threatened."Of course, how the pandas and other animals in the Zoo would be affected is one of the primary concerns and animal care staff have already made the rounds to check on the animals, and the pandas were in their bedrooms, they did not appear to even know anything was going on just a little bit north of them," said Zoo Spokeswoman Christina Simmons.Power was out at the nearby Canyon Cafe. It is expected to remain closed Monday according to Zoo officials.The Zoo will open and operate on a normal schedule.