District Mahila Court Judge Thirunavukkarasu also slapped a fine of Rs 10,000 on Anandharaj.
The prosecution case was that Anandharaj (45) of Karungalpalayam in the district was having a physical relationship with his sister-in-law, a speech and hearing impaired lady living with her younger sister.
They submitted that Anandaraj and the woman often used to go to the Cauvery river to wash clothes. On May 21 last year, the couple went there at night when the woman insisted that he marry her. This angered the man who then strangulated her to death with a piece of cloth, smashed her head with a big stone and left the area.