The couple's son, Fredrick Karomo, said he was sleeping when he heard a bang in their compound. He hurriedly woke up and went out to see what was happening. He found his parents' house had been flattened.
"I was met by a cloud of dust and debris when I woke up. I thought a bomb had been hurled into our compound. Later, I realised my parents' house had been flattened by falling debris," Fredrick said.
"I started screaming and I was joined by neighbours who helped me call the Kiambu County fire brigade and the police," he added.
"I moved closer and realised my parents were under the rubble. I tried calling them but there was no response. I stood there helplessly. It was a horrifying scene for me even as more and more neighbours streamed into the compound to help us."
After about one hour, the fire engine and an earth mover arrived and started removing the debris as the officials tried to save those trapped in the building.
The victim's house was completely destroyed.
The fire brigade personnel was later joined by their counterparts from the Kenya Red Cross Society when the two bodies were retrieved.
Screams rent the air as inconsolable family members and neighbours tried to come to terms with the incident.
The police had a hard time controlling the surging crowd.
Kinuthia Karomo said the death of his elder brother and his sister-in-law were major losses to the family.
"I am an architect and I could foresee a problem. We tried to stop this construction but we were unsuccessful. The County Government of Kiambu has marked it twice as not fit and even arrested the workers twice. But every time they were arrested, they would come back and continue with their shoddy job," Kinuthia said.
He added: "We believe the owner of the collapsed building is connected to some powerful people. That is why he was allowed to continue constructing a faulty building."
"The impunity with which the owner of the ill-fated building is operating is beyond anyone's comprehension. They would construct a slab and without giving it ample time to dry and cure, they would go ahead and start constructing the next floor."
"There was a time I looked at the building and doubted the workmanship. I knew we were courting disaster," he said.
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Kinuthia claimed the building's owner sent away the engineer and architect and decided to work with local artisans.
Susan Njeri, a neighbour, called on the government to implement the law on construction to avert deaths.
"This week alone, a house in Kasarani caved in and even before the rubble is cleared another one kills people here. And these two houses collapsed just days after a similar incident in Kirigiti. This can only mean that the National Construction Authority, the Kiambu and Nairobi county governments, and the police are not doing their jobs," Njeri said.
George Ngugi from the Kenya Red Cross said another person who suffered slight injuries was taken to a nearby hospital.
Kiambu Governor Kimani Wamatangi said they will bring in machines to clear the site.
"This is sad, and it is coming just a few days after another tragic incident at Kirigiti where a woman and her two children perished after a house collapsed," Wamatangi said.
The governor said he has consequently suspended the Kiambu County board responsible for checking and approving buildings.
"The board has a lot of weaknesses that have been allowing these kinds of constructions to come up. The situation has been made worse by the fact that when an arrest is made, the culprits always end up being released to continue their illegal activities," Wamatangi said.
He pleaded with the courts to help the fight against the vice by not granting anticipatory bail to the suspects.
Meanwhile, the police are looking for the owner of the building.