Justice Jessie Lessit on Monday ordered a trial within a trial in the murder case of lawyer Willie Kimani.
This is after the defence objected to the confession statement produced by the prosecution.
The 21-page confession was allegedly recorded by police informer Peter Ngugi, the fifth accused in the case.
Kamau was coerced and tortured by police to sign the alleged confession, the defence claimed.
The prosecution told the court they intend to call six witnesses to prove that Kamau gave the confession that incriminated most of the suspects in the case.
Geoffrey Kinyua, the officer who recorded the statement, was the first to take the stand and he defended the statement.
He said it was genuine and was narrated to him by the suspect on August 9, 2016.
Five police officers were accused of hatching a plot to mercilessly kill Kimani, his client Josephat Mwenda and driver Joseph Muiruri on June 23, 2016.
Read:
See:
They include Fredrick Leliman, Leonard Maina, Stephen Chebulet, Silvia Wanjiku and informer Peter Ngugi.
The bodies were found stashed in gunny bags in a river in Ol-Donyo Sabuk, Machakos County.
A diver who found the bodies earlier told the court of his two-day horrific experience.
John Mwaniki said the bodies were tied at their waists, while their heads had been tied with plastic bags.
The bodies had started decomposing and blood oozed from their mouths and noses. Mwaniki told Justice Jessie Lesiit he had gone for a bath in the river when he saw “a strange thing” floating. He decided to go closer to find out what it was.
He saw legs protruding from a gunny bag. “I swam out immediately to call my friend Patrick,” Mwaniki said.
The two friends agreed that Mwaniki would rush to call the police while Patrick would watch over the body. He reported, but police did not take action, he says.
The following day, Mwaniki and his friend went back to the scene and were shocked to see a second sack floating a few metres away from where the first body still remained.