Nakuru East sub-county Police Commander Mohammed Wako said they were holding the couple for interrogation.
"We came to know about the body when Boniface Mungai (the son of the deceased) came from Gatundu on Wednesday and reported the matter," Wako said.
"Our Scene of Crime detectives visited the scene and recovered the body which was badly decomposed, we sent the body to Nakuru County Hospital mortuary for a post-mortem," he added.
Wako said they were yet to establish the cause of the death and why the family stayed with the decomposing body for that long.
Mungai said his uncle David Kinyanjui invited his sister, Wahu to visit him in Nakuru on January 15 so that she could meet his third wife.
"Kinyanjui had just married his third wife and wanted to introduce her to his sister (Wahu). We made arrangements for her to travel from Gatundu to Nakuru. She arrived on January 15," he recalled.
Mungai and his mother were in constant communication until January 29 when it stopped.
"When we tried to inquire from Kinyanjui what the problem was, he told us not to worry and that mum was well but she had dropped the phone in water and it was damaged," he told The Standard.
When Mungai insisted on having a conversation with his mother through Kinyanjui's mobile phone, he started giving excuses.
YMCA estate residents in shock at the home where the decomposing body was discovered. [Kipsang Joseph, Standard] "On Tuesday evening, I insisted on just hearing my mother's voice, but my uncle told me to wait and then he disconnected the call," he said.
Coincidentally, one of Kinyanjui's neighbours called and informed Mungai of a foul smell emanating from his uncle's house. "The neighbour told us of the foul smell like that from a decomposing body emanating from the house and we got alarmed," he said.
It was at this point that Mungai realised that something was not right and he decided to travel to Nakuru in the company of his other uncle, Zack Wanjohi to establish what was happening.
"We started the journey to Nakuru on Wednesday at 2 am and we arrived at the home at around 4 am," Mungai said, adding that they were allowed into the house at 6 am.
They found Wahu's body tucked in bed and flies were all over the room. "It appeared that my mother might have died two or three weeks ago. The smell was strong and flies were all over," Mungai said.
Stay informed. Subscribe to our newsletter
Penninah Wambui, a neighbour, said when they inquired from Kinyanjui about the smell, his wife told them that it was from a dead dog.
"It is unbelievable that the family stayed with a decomposing body in the house for that long without reporting to the police. Everything seemed normal to them. They never complained," she said.
Wambui, who has been the couple's neighbour for 24 years, said it was shocking that no one from the family was mourning.