Sudhakar Saroj, who was a former employee of the shop, along with his brother Diwakar Saroj and Shamsher Alam, were arrested yesterday evening for the robbery in Sarita Vihar, they said.
A country-made pistol and cash was recovered from them, they said.
The arrests were made on a complaint filed by Ashok Prasad, employee of the shop, that a masked youth had robbed Rs 80,000 from the store at gunpoint, they said.
Prasad told the police that the assailant seemed to know where the cash was kept, leading cops to suspect that a current or former employee of the store was involved in the crime, they said.
Alam, a co-worker who was present in the store at the time of the incident, was in contact with Sudhakar who had left the store two months back, they said.
After Alam was arrested, he told police that Sudhakar and his brother Diwakar were the brain behind the incident and they gave him Rs 10,000 for his cooperation.
The two accused were then arrested, police said.