Justice Jessie Lesiit ruled at the Milimani Law Courts in Nairobi that the respective sentences will run concurrently.
The judge said the four killed lawyer Willie Kimani, his client and driver in the "most foul" circumstances.
Lesiit directed the correctional facilities' management to consider the period the convicts have spent behind bars during trial and deduct from their overall respective sentencing.
Leonard Mwangi, who was the fourth accused, was in June 2022 acquitted over lack of sufficient evidence against him.
On July 22, 2022, while rendering a guilty verdict on the four, Justice Lesiit said that the accused, who were police officers at the Mlolongo Police Station, contemplated for three hours on whether to kill the victims on June 23, 2016, a contemplation that she said indicated malicious motive.
"I have carefully considered the entire evidence adduced in this case by both sides and as well as the submission by both counsels. Having done, so I find that the circumstantial evidence established against the first, second, third and fifth accused persons justifies the guilt of the accused beyond any other reasonable hypothesis besides that of guilt," said Justice Lesiit.
Leliman, Cheburet, Wanjiku, Mwangi and Ngugi had been accused of abducting Kimani and his co-victims on their way home from attending a case at the Mavoko Law Courts that had implicated Administration Police Officer Leliman, the first accused.
The prosecution, which produced 46 witnesses in court, said Leliman had unlawfully arrested and shot Josephat Mwenda, a boda boda operator, in April 2015.
Leliman took Mwenda to the Mavoko Law Courts, where he was charged with being in possession of bhang, resisting arrest and gambling.
An aggrieved Mwenda reported the matter to the Independent Policing Oversight Authority (IPOA) and sought help from the International Justice Mission (IJM).
It was Mwenda's action that angered Leliman as he felt his job was on the line after IPOA took up the matter and the officer was summoned for questioning.
IJM also came on board and tasked Willie Kimani to defend Mwenda in the case at Mavoko Law Courts.
On the fateful day of June 23, 2016, the three appeared in court for a hearing, not knowing it would be their last day alive.
Ngugi confessed that after the killings, the bodies were put in gunny bags, stashed in two car boots, and dumped in River Athi at Ol-Donyo Sabuk, Machakos County.
The prosecution's closing remarks were that they had proved the offence of murder against the five accused persons beyond any reasonable doubt, backed by the evidence of 46 witnesses and 117 pieces of exhibits.
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However, Justice Lesiit said the fourth accused, Leonard Mwangi, put up a spirited defense of his innocence.
The other four accused persons had equally made a strong case to prove their innocence and produced several exhibits with 15 witnesses on their side.
However, the judge said the prosecution presented watertight evidence that implicated the four, with Leliman as the star player in the murder plot.
"The evidence is overwhelming that the first accused (Fredrick Leliman) personally attended to ensure that the deceased persons were captured, detained to await nightfall, murdered and their bodies dumped or flung into the river to make it difficult to recover them," said Justice Lesiit.
A post-mortem report by chief government pathologist Dr Johansen Oduor, which was also used as evidence in the case, showed that Willie Kimani and his co-victims were killed through blunt force trauma on their heads before being strangled.