Cambridge City Councilor David Sullivan criticized the state fire marshal's office yesterday for failing to determine the cause of two suspicious fire's that took place at a Mass Ave. apartment building last spring.

The two fires, which occurred within a one-month period, gutted the old Francis Allyn House at 1564 Mass Ave.

Sullivan labeled the state investigation "inadequate." He said he had not been able to learn of any progress in the investigation despite repeated conversations with the marshal's office.

The state officer assigned to the case was not available for comment yesterday but has previously declined comment.

Sullivan has previously charged that there is strong circumstantial evidence that the owner of the rent-controlled building had it torched in order to escape the city's strict housing codes. Sullivan said he is concerned that the fires might set an example other landlords might be tempted to follow.

Steven Bell, the owner of the building, was not available for comment yesterday. Bell has publicly denied responsibility for the fires, saying he had nothing to gain from them.

The two fires took place on April 28 and May 27 of this year.

Before the first fire, Bell applied for a permit from the city's Rent Control Board to remove the units from the market and upgrade them to luxury condominiums. Sullivan argued that the fires might have made the board more likely to grant the removal, because the units had become unoccupiable.

The rent board denied Bell's petition anyway on September 3 because the Cambridge Housing Authority (CHA) expressed interest in buying the property.

The CHA is currently negotiating a sale price with Bell. Sullivan said. He added that the city could take the property by eminent domain if Bell and the housing authority fail to reach an agreement.

Built in 1832, the Francis-Allyn House was declared a "protected landmark" by the City Council in 1980.