The shocking sexual assault unfolded around 2 a.m. July 27 when the woman entered the stairwell of her building in Belmont and was approached by an unknown man from behind, cops said.
The man, wearing a black mask and another red plastic face covering, pulled out a firearm and raped the woman, cops said.
The man then fled.
The woman did not report the attack until Monday and was treated for injures at BronxCare Health System Hospital, cops said.
Police released surveillance footage Tuesday of her suspected attacker.