The sources claimed that the militants used the forest area located behind the Army camp to gain entry.
The area has barbed wire and a small wall, they said.
Two Indian Army officers and five jawans were killed in an eight-hour long gun battle at the military camp near the Army's 16 Corps headquarters in Nagrota on November 29. Three militants were also neutralised in the attack.
The Army unit is located just three kms from the Corps Headquarters at Nagrota.
A statement by the Army soon after the attack had said that the terrorists forced their way into the Officers Mess complex by throwing grenades and firing at the sentries.
However, Army chief Gen Dalbir Singh Suhag said here on the sidelines of an event that the incident was under investigation and a final report will clarify everything.