The Directorate of Criminal Investigation (DCI) officers established that Lawrence Warunge, 22, the prime suspect in the murder of five of his family members in Kiambu County tricked the girlfriend into aiding him to commit the crime.
Detectives from the Homicide and the Crime Scene Investigations Unit detailed that the university student had planned to wipe out his family using carbon monoxide before opting for using the knife.
Warunge tried to execute the gas strategy thrice but failed and then hatched a plan to use the girlfriend, Sarah Muthoni.
He promised the lady that he would make her life better and ensure that the two lived in peace for the rest of their life.
Warunge asked the girl to purchase a nine-inch knife with a metallic handle in Thika, which he used to stab his father and murder his mother, two siblings.
He reportedly attempted to convince Muthoni to drink alcohol and smoke bhang, but his efforts backfired as the lady declined, having never induced drugs ever before.
The prime murder suspect had expected that the girl would pass out as he rushed to his rural home, Ndũndũ village, Karura Ka Mũrĩmo, Kiambu county, to execute his plan.
Detectives are, however, trying to unravel why she hosted him at the rental house in Jikaze, Mai Mahiu, a house they moved out of a day after the gruesome murders were committed. The two relocated to a hideout in Lower Kabete.
The sleuths added that they had not found incriminating evidence against the lady, other than purchasing the knife used in the murder plot.
"A confession (by Warunge), standing alone, is not enough for a conviction. A thorough investigation has just commenced,” a senior detective said.
Warunge confessed to committing the murders after watching a TV series dubbed Killing Eve. This prompted the court to order police to detain him and the girlfriend for 14 more days to pave way for investigation.
The prosecution argued that he was a flight risk and would attempt to murder his two other siblings who were in school.
The court also obliged to the government's request to have the two suspects undergo mental assessment, adding that the case will be mentioned on Monday, January 25.
