It was a deathtrap. The Brooklyn building where five people died in an arson was illegally divided - and the partitions made it impossible for several victims to escape, officials said Friday. The Buildings Department issued three violations against the Bensonhurst building's landlord, who could also soon become the target of a criminal probe, according to law enforcement sources. Three illegal walls were installed on the 86th St. building's overcrowded third floor, where up to 15 people lived, officials said. Those walls created only one way out for many of those residents - the stairwell that was filled from smoke...