Vitas Jasionis was found guilty of raping the woman
A watchdog will investigate after police allegedly left a woman with her rapist while responding to a 999 call.
Two officers went to the victim's flat in Woolwich, south-east London, but allegedly made no inquiries after rapist Vitas Jasionis reassured them.
Hours later the woman was raped again. The Independent Police Complaints Commission (IPCC) will investigate.
IPCC Commissioner Deborah Glass said Jasionis's trial raised "serious concerns" about officers' actions.
Jasionis, 54, from Southwark, was found guilty of raping the 32-year-old woman at Woolwich Crown Court last week.
The court heard that Pc Matthew Harris and another officer went to the flat in Ruston Road after a neighbour reported a woman screaming.
When he knocked on the door Jasionis answered and reassured Pc Harris, who then allegedly left without making further inquiries.
Hours later the victim called the police but by then she had been raped again, the court was told.
Jasionis was arrested at the scene. He will be sentenced at a later date.
Pc Harris has already been referred to the directorate of professional standards.
The IPCC said on Monday that it will conduct an independent investigation.
Ms Glass said: "This woman suffered a horrific attack and people are understandably asking whether the police could have done something to help her.
"The trial of Jasionis clearly raised serious concerns about the actions of the officers who responded to the original 999 call."
The IPCC will examine their actions as well as the overall police response to neighbours' calls.
The inquiry comes after the IPCC warned that officers could be prosecuted for making blunders in two serial sex attacker cases - street stalker Kirk Reid and taxi-driving rapist John Worboys.