Officials say 29-year-old Victor Arias started the blaze that took the lives of three people and injured more than a dozen others.
Arias was arrested Monday on charges of criminally negligent homicide.
In addition to the three people who were killed, five people were left in critical condition after the fire, including several children.
Prosecutors say seven residents are still hospitalized.
The fire broke out on the first floor of the six-story residential building around 12:30 in the morning last Monday.
Dozens of residents were trapped on fire escapes when firefighters arrived.
FDNY investigators say the suspect deliberately discarded a lit cigarette into cardboard boxes, causing them to ignite.
That fire then quickly spread through the common hallway and then a stairway of the building, rocketing up through the roof.
Investigators say Arias lived in the Dyckman Street building his entire life with his mother and sister.
He has never been arrested before and he declined comment as he left his arraignment.
Arias was released in part because prosecutors say he did not intend to burn the building down.
He is due back in court on June 5. Until then, he cannot travel outside the city, must abide by a curfew, and will be subject to electronic monitoring.
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