Businessman Slavi Binev has been killed in Pavlovo, a district of Sofia. Investigators are mainly looking at a row over unsettled money matters.
They believe the evidence so far does not point to a contract killing, and say the dispute may have flared up on the spur of the moment.
One of the detained men has known Binev for years. They are linked through taekwondo.
The detained man's wife is an architect and the daughter of Stoyan Yanev, a former chief architect of Sofia. She is Binev's business partner in the construction company Evinko Ltd. She and her husband also own Polanta, a firm dealing in gemstones and precious metals.
Within hours of the killing, details emerged about the shared business and personal ties between the three. According to unofficial and unconfirmed information, the detained man's wife had an intimate relationship with Binev, so a personal motive is also being considered. Police have not said they are checking such a theory. There is no information that any charges have been brought against her.