Mugithi singer DJ Fatxo is the key suspect in the death of Jeff who allegedly fell from the 12th floor of a building where the singer lived.
Mwathi's body was last week exhumed.
This was after Inspector General of police Japhet Koome said they have found gaps in the incident and hence need to exhume the body to help their probe.
Detectives handling the case noted in their preliminary findings that Mwathi did not die by throwing himself from the12th floor of a friend's apartment in Kasarani as previously reported.
According to Citizen TV, detectives established that there was a scuffle in the house of key suspect Lawrence Njuguna alias Dj Fatxo after a forensic examination of the house.
DCI detectives who took over the case from Kasarani police believe Mwathi was killed before he was thrown from the apartment's rooftop in the wee hours of February 23.
They dismissed claims that the 23-year-old threw himself from Fatxo's bedroom window since the window grills are too small for a person to go through.
Fatxo, who termed Jeff as his good friend, has since denied involvement in his death and said he will cooperate with investigators.
He told the Media on March 12 that he was the one who reported to the police about Jeff's disappearance on the morning he died.
This was after he left in the company of three ladies but returned hours later but did not find Jeff in the house.
"I'm so willing to cooperate with the detectives, DCI until we all know what happened to Jeff," he said.
"For Kenyans and my fans, keep praying for me, this is hard but we will emerge victorious," he added.
Detectives said on Friday the next phase of the investigation will see them question three other people who were in the house the night Jeff died.
Officers from the Kasarani Police station who were the first at the scene of the crime will also be questioned.
Jeff was buried on March 3 in Nakuru County.
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