A probe into the leakage by the Prime Minister's Office (PMO) has also cleared Gen Singh of any wrongdoing in the episode, highly-placed sources told PTI here.
In his letter, the Army Chief had highlighted the critical shortage of equipment and ammunition in artillery and armoured regiments.
The female officer belonging to the Indian Economic Service (IES) was handling the charge of intelligence agencies under the Cabinet Secretariat and was nailed after interrogation of some suspected persons, they said.
The officer has now been repatriated to her parent cadre and further action can be taken against her for leaking such a sensitive document, sources said.
After the letter surfaced, both the Houses of Parliament were rocked over the issue and certain parties had demanded action against Gen Singh also.
At that time, Gen Singh had said that incident should be treated as "high treason" and the source of leakage should be dealt with "ruthlessly."
"The leakage of the letter should be treated as high treason. Cynical approach to tarnish my reputation should stop. Sources of the leakage should be found and dealt with ruthlessly," Gen Singh had said in a statement issued by the Army Headquarters.
Following the incident government had asked the Intelligence Bureau (IB) to investigate the matter and find out the person responsible for it.
The letter was leaked to the media after Gen Singh made a sensational disclosure in an interview that he was offered a bribe of Rs 14 crore by a retired Lt General for favouring a sub-standard defence deal regarding purchase of Army trucks.
