ARLINGTON, Wash. -- Police have arrested a 53-year-old woman for arson in connection with Monday's fire that destroyed a commercial building in downtown Arlington.

Investigators discovered a small space at the back of the commercial building that was being used as a residence. Detectives interviewed the "tenant" and learned that he and the suspect - his estranged wife - had argued earlier that evening. Fifteen minutes after they argued, she reportedly called him and threatened to burn down his residence. Evidence obtained confirmed she had returned to the building later that evening.

The woman from the Arlington area was being booked into the Snohomish County Jail on one count of arson in the first degree and domestic violence.

More: Woman arrested for arson in downtown Arlington fire

One of town's oldest buildings destroyed

The two-alarm fire damaged one of the town's oldest buildings.

Firefighters were called to the scene at North Olympic Avenue and East Second Street shortly after 7 p.m. Nearly 50 firefighters responded to the call for help.

Kristin Banfield, an Arlington spokesperson, said it was a "substantial" fire that was reported on the second floor of a commercial building that includes 2 Bits & More Thrift Shop. That store was destroyed.

Chris Nelson of Arlington was riding BMX bikes with a friend when he saw the flames. Crews arrived at the same time Nelson pulled up to a corner near the fire.

“The pressure and whatnot actually blew out the front windows,” Nelson said. “It shot like a six foot flame real quick, and it got pretty gnarly.”

Nelson said the window blowout sounded like six M-80s strapped to each other.

A city council meeting was taking place right across the street when the fire started. Banfield said many inside city hall heard the explosion, and came outside to see what it was and call 911.

Firefighters arrived on the scene within one minute, because the fire department is also right around the corner.

Video: Window explodes during Arlington fire

No injuries have been reported, but about 10-15 residents who lived in the adjacent apartments have been displaced.

The building is one of the oldest on Olympic Avenue, built in the late 1800s-early 1900s, and has had many remodels since, which Banfield said made the fire so difficult to fight.

"As we're going through and trying to put out the fire, we're finding additional voids from prior remodels, so different pockets where there could be fire," Banfield said.

Crews do not know exactly where or how the fire started. The fire marshal will lead that part of the investigation.

Olympic Avenue is blocked between Second and Fourth Streets.

Photos: Downtown Arlington fire