The CBI case was that George had allegedly amassed huge wealth after 1990 which included commercial and residential properties in posh South Delhi area, properties in Bangalore, Chennai, Kerala and agriculture land bordering Delhi besides cash over Rs 1.5 crore in bank accounts.
The CBI had alleged that George had purchased assets using money received from abroad which he claimed to be gifts from his family members.
CBI sources said agency had sent judicial request to the United States seeking details of remittances which were allegedly received by George but it got only part information which could not be translated as evidence.
The sources said these transactions were suspected to be hawala in nature as the alleged illegal gratifications were first taken abroad and returned as gifts which was white money for George.
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The sources said the agency did not get complete response from the US authorities about these transactions which left it with insufficient evidence to proceed with the filing of charge sheet against George.
CBI had also sought details of "business transactions" by two firms which were allegedly run by George's wife as they were suspected to be another route for converting alleged illicit wealth into white money.