After nearly 19 months of its preliminary enquiry into telecom spectrum allocation during 2001-07, the CBI has closed the probe pertaining to the period when Arun Shourie was the telecom minister.

CBI sources said the documents related to tenure of Shourie and his examination during the probe have not revealed any irregularity.

After registering the preliminary enquiry in January, 2011, the CBI had found alleged irregularities during the tenure of two ministers -- late Pramod Mahajan and DMK leader Dayanidhi Maran -- in which it had filed FIRs.

The probe was spanned across telecom spectrum allocation during 2001-07 in which Shourie was in charge of the telecom portfolio between January 2003 and May 2004 in the NDA government. Before him, Mahajan was telecom minister in the NDA government.

After the UPA government came to power in 2004, Maran was the telecom minister till 2007.

CBI sources said the first-come, first-served policy adopted during Shourie's tenure was to promote telecom services in less lucrative areas where telecom operators were reluctant to go.

The agency has found in its probe that during his tenure the licences were mostly given to non-attractive regions like northeast, Odisha, Jammu and Kashmir.

During its probe, the agency scrutinised meetings chaired by Shourie, observations of Shivraj V Patil committee besides other documents only to conclude that no irregularity was committed during his tenure.

The agency has booked former telecom secretary Shyamal Ghosh and three private cellular companies for alleged irregularities in awarding additional spectrum during Mahajan's tenure while Maran has been named in Aircel-Maxis deal probe.