Rajendra Garg, a dealer of a multinational food and beverage company, his brother Ramesh and their employee Kamal Dev, left their office in Kakrola village yesterday, they said.
While they were going towards Najafgarh Road, a biker accidentally touched their car following which they had a heated argument, the police said.
Mr Garg, 50, who was behind the wheel, was allegedly shot at by the pillion rider, they said.
The man, who was on the motorcycle, allegedly attacked Ramesh, 54, on his head with an iron rod, the police said.
The pillion rider allegedly shot at Kamal Dev, who was in the backseat of the car. They also took a bag containing Rs 3.5 lakh, they said.
A passer-by, who tried to intervene, was threatened by the accused who fled after firing in the air, the police said.
Mr Garg was declared brought dead while his brother and Dev, 34, were out of danger, they said.
Initially, it was suspected that it was a case of robbery-cum-killing, but during investigation it emerged that an ex-employee was involved in hatching the conspiracy.
The main accused, who is a juvenile, hailing from Ghaziabad, was allegedly nursing a grudge against his former employers, after he was sacked over poor performance over a month ago, the police said.
He contacted his friend, who subsequently contacted his acquaintance, and they involved three others, in the plan, they said, adding that all the accused were arrested.
The accidental touching of the motorcycle with the victim's car was part of a plan, they said.
The police have seized two weapons, 18 cartridges, two motorcycles and two knives from the accused.