CBI has closed the case of disproportionate assets against Congress President Sonia Gandhi's aide and former personal secretary Vincent George as it could not get enough evidence.

The sources said the agency's judicial requests seeking evidence from the United States remained unanswered for nearly 10 years, prompting the agency to close the case citing lack of sufficient evidence to pursue the case.

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.

George had allegedly purchased assets using cash received from abroad which he claimed to be gifts from his family members.

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.

The sources said the agency could not get response from US authorities about these transactions which left it with insufficient evidence to proceed with the filing of chargesheet 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.

They said the agency had pursued with the US authorities since 2002 to furnish the information but could not get any, resulting in withdrawal of the case.