In a shocking incident, a 90-year-old widow, who is a cancer patient, has been raped here in Kerala by a man who was armed with a knife, police said on Wednesday.The woman too told the media that the crime was committed by someone who knew the layout of her house."The accused entered my house through the back door. This can be done only by someone who knows the house well," she said. "I pleaded with him not to harm me but he did not listen... I want the police to arrest the accused," she said.The crime took place five days ago but became public knowledge only on Wednesday.Kollam Rural Superintendent of Police Ajitha Begum told the media that police officials had taken the victim's statement."An FIR has been registered. We will probe the incident by speaking to her relatives and those who met her after the incident," said Begum.