The Directorate of Criminal investigations has grilled 101 individuals in the probe on Mathira MP Rigathi Gachagua.
According to the DCI, 22 companies are said to have been beneficiaries of Ksh12 billion in tenders from the national and county governments.
Detectives have extended investigation into politicians allied to Deputy President William Ruto who are said to have received part of the loot.
According to the DCI, former Agriculture CS Mwangi Kiunjuri, Laikipia Senator John Kinyua Nderitu, Meru Senator Mithika Linturi and Ruguru MCA Karanja Muriuki are some of the politicians under investigation.
Rigathi, who rose from a district commissioner to President Uhuru Kenyatta's PA and finally an MP, is alleged to have exploited his vast networks to bag tenders in different counties.
Detectives have visited various counties to establish how the MP was awarded the suspicious contracts.
DCI officials visited Kwale to probe the award of an incinerator tender, Bungoma over a medical equipment contract, Nyeri for dialysis medical equipment and Kisii for the supply of ambulances.
He is also said to have received tenders from the Ministry of Lands, State Department for Planning, Ministry of Health, Mathira CDF, and the National Irrigation Board.
The High Court has frozen more than Ksh200 million belonging to the MP, lifting the lid on his financial war chest.
In his defence, he claimed that he was being targeted maliciously for his support of Deputy President William Ruto.
"It is a scheme meant to harass and intimidate me over my political stand," he told the media.
The Assets Recovery Agency was earlier unable to trace Ksh5 billion which had been allegedly deposited into bank accounts linked to the Mathira MP.
According to documents filed in court by ARA, the MP reportedly received the Ksh12.5 billion in suspicious payments since 2013.
The Agency stated that Ksh7.3 billion had been withdrawn or transferred from the accounts in question and could be supported by relevant documents. However, a deficit of Ksh5 billion which could not be supported by withdrawal or transfer documents.
