UPDATED 12/24/10 3:54 p.m.

CHICAGO (CBS/WBBM) — The fire in South Shore that killed two Chicago firefighters this week was set inside the building, according to fire officials.

The Office of Fire Investigation determined Friday that someone had set fire to wood or garbage inside the building, touching off the blaze at 1744 E. 75th St. that killed firefighters Edward Stringer, 47, and Corey Ankum, 34.

Gas and electric service at the former Banner Laundromat and Dry Cleaners had been off for many months.

Police have now launched a criminal investigation, fire officials said.

LISTEN: Newsradio 780’s Mary Frances Bragiel Reports

After talking to several homeless men and women in the area, investigators say the abandoned building was at times used as a shelter from the cold.

Stringer and Ankum were killed in the fire Wednesday. A wall and roof collapsed on top of them as they searched through a vacant burned-out building, out of concern that homeless people might be inside.

It turned out that the building had a history of code violations. The most recent time city inspectors looked at the building, they found 14 code violations and said building owner Chuck Dai had failed to maintain it “in a structurally safe and stable condition.” Two code violations related to the roof, including failure “to maintain roof in sound condition and repair.”

While the back of the building had a bow-string truss roof, which poses a danger of collapsing during a fire, Chicago Fire Commissioner Robert Hoff said firefighters decided to go in for a precautionary search anyway because the fire started in an office area far from the ceiling.

Meanwhile, Chicagoans have shown an outpouring of grief for the fallen firefighters. Family and friends gathered outside Ankum and Stringer’s homes Thursday night for private memorials, as the giant flags in Daley Plaza flew at half-staff over the Christkindlmarket celebration.

Bragiel reports a Facebook page has also been set up, titled, “In memory of Chicago Firefighters Corey Ankum and Edward Stringer.”

More than 14,000 people have quickly become fans.

But those hoping to pay their respects in writing will find this message: “Thanks for visiting the page. Due to a very sick and aggressive person posting inappropriate pictures and comments, we have temporarily disabled comments and posts.”

While nothing further was specified about the comments or their content, a separate wall post suggested that the person responsible also posted pictures and comments mocking the death of Derek Lodestein, 16, who died this week after falling through the ice on a lake in southern Indiana.

The Facebook page says the FBI and the Bureau of Alcohol, Tobacco, Firearms and Explosives have been notified about the inappropriate comments, and indicated that as of early Friday, comments had been enabled again.

LISTEN: Newsradio 780’s Mary Frances Bragiel Reports

A total of 17 other firefighters were injured in the Wednesday morning fire. As of Friday morning, officials said at least five were still hospitalized.

Meantime, visitation for Stringer will be held from 3 to 9 p.m. Monday at Blake Lamb Funeral Home, 4727 W. 103rd, Oak Lawn.

Stringer’s funeral will be at 10 a.m. Tuesday at St. Rita of Casia Shrine Chapel, 7740 S. Western.

Arrangements are still pending for firefighter Corey Ankum.

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