Toronto police say arson caused a fire that destroyed a heritage building at Yonge and Gould Streets last month.

The six-alarm fire broke out Jan. 3 at 335 Yonge St., the historic building that housed popular Thai restaurant Salad King and several other businesses. The building had been unused and surrounded by security fence since April, when a portion of its brick facade crumbled onto the street.

Police have since determined that an arsonist caused the blaze, Toronto Police Const. Tony Vella confirmed Monday. He said they are still trying to identify a person seen in a security video recorded the night of the fire.

When interviewed last month, local councilor Kristyn Wong-Tam said it's unlikely the fire was started by squatters, as it would have been difficult to access the building through the security barrier. She said the building's gas, power, hydro and water had been shut down after the wall collapsed.

The Office of the Ontario Fire Marshal said it appears the blaze began on the second or third floor.