The accused, A Rajesh, and Ms Swati allegedly killed the latter's husband Sudhakar Reddy at his house in the district headquarters town of Nagarkurnool on November 27, according to police.
After the killing, the duo dumped the body. The physiotherapist then himself inflicted injuries on his face to pose as the Ms Swati's husband Mr Reddy, and got admitted in a private hospital, they said.
Mr Rajesh was arrested today from the hospital where he was undergoing treatment since November 28, Nagarkurnool Circle Inspector Srinivas Rao said.
Last month, the accused had drugged Mr Reddy with an injection and he along with the woman hit the victim on his head with a sharp object, killing him on the spot. The duo then dumped the body in a forest area of Mahabubnagar district and set it on fire, a police official earlier said.
The woman later lodged a police complaint claiming that four unidentified persons attacked her husband at their house, poured petrol on his face and other parts of the body and set him on fire, he had said.
As a part of their conspiracy, Mr Rajesh, to whom she got attracted when she visited his clinic two years ago, poured kerosene on himself and burnt his face and upper part of the body, to "pass off" as Mr Sudhakar, inspector Rao said.
Ms Swati then got Mr Rajesh admitted to the hospital as her husband Sudhakar Reddy, he said.
She was allegedly having an affair him and wanted to live with him by getting rid of her husband, he said.
"The woman said she did not want to run away with Rajesh as she had children. They then hatched a conspiracy to eliminate Reddy and enacted the entire drama," Mr Rao said. However, Mr Reddy's brother and other family members grew suspicious after seeing the behaviour and appearance of the patient (Rajesh), whose burns too had healed by the time, at the hospital.
They then approached the police last week complaining that the person was not Mr Reddy, following which police questioned Ms Swati, who confessed to the killing plot hatched by her and Mr Rajesh.
The woman was arrested on December 10.
Mr Rajesh and Ms Swati have been booked on charges of murder under relevant IPC sections, the police inspector added.