Two of the four accused -- Allanoor (23) and his cousin Raees (25)-- were arrested last night for the murder, Aerodrome Police Station In-Charge K L Dangi said.
The other two accused, Amzad (18) and Devilal (25), are still absconding, police said adding that they belonged to the neighbouring Dhar district.
40-year-old Arman Patel was found dead near Super Corridor in the city on September 23. He was a native of Matana village in Ujjain district.
"The deceased had an affair with Salma, the married sister of the accused. When her husband Ansar came to know about it, he sent her back to her parents' place at Gunavda village in Dhar district. However, her affair continued," a police officer said.
According to the police, as soon as Arman came to the place, they tied his hands with a rope and hit him with a stick to kill him.
Later, they took his body on their motorcycle to Super Corridor area in Indore and dumped it on the road to give an impression that the victim has been killed in a mishap, police said.