The incident took place at around 1.30 AM when the accused R H Yadav (49) shot dead his two colleagues - H K Singh (52) and Somdutt (53) - and left two others seriously injured after he fired seven rounds from his self-loading rifle at the Air Force station in suburban Santacruz, said Sudhir Jambhavdekar, senior inspector at Nirmal Nagar police station.
Singh was his guard commander who prepared duty charts, police said.
"Yadav was harassed by his colleagues and he was not on good terms with them. He was frustrated because of which he opened fire," Deputy Police Commissioner Namdev Chavan said.
The injured, identified as C B Thapa (46) and Bheem Singh (51), were undergoing medical treatment, police said.
Yadav was arrested from suburban Goregaon while he was trying to escape in an autorickshaw.
According to police, Yadav was aggrieved with his colleagues who used to make fun of him.
"Even after he was scheduled to do day duty, his schedule got changed to night duty, making him to lose his cool. Many a times, he expressed his dissatisfaction to his seniors but in vain. Moreover, staff members used to make fun of him for no reason," said another police official.
At about 1.30 AM, he walked into the guard rest room where he shot Singh and Somdutt in their chests, killing them on the spot, police said.