On Thursday, Imad and Bahaa Dawara pleaded guilty to conspiracy to commit arson and conspiracy to defraud the United States.
The siblings were charged after their hookah bar and lounge at 2nd and Chestnut streets went up in flames in February of 2018, causing more than $20 million to the retail block.
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The blaze destroyed a neighboring business and gutted two mid-rise buildings, leaving 160 people homeless. A number of pets also died.
Officials say the brothers set the fire for insurance money, following a dispute with their landlord. Federal prosecutors say the Dawaras had taken out $750,000 in insurance weeks earlier.
The Dawaras, who used gasoline to start the blaze, would serve nine years in prison and pay $22 million in restitution under terms of the plea agreements entered Thursday. Their sentencing is set for June.
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-- The Associated Press contributed to this report.