Gennady Gribovsky, the 60-year-old director of AS Viru Kaevandus, was shot dead in the town of Johvi late on the evening of July 21.
Regional criminal police superintendent Alexander Zhegulov told the daily Eesti Paevaleht the man was murdered upon his return from his summer cottage.
"He had with him about 1 million kroons' worth of cash in Estonian kroons and foreign currency which he left in his apartment. He also left his gun there and then went to put away his car. That's when he was shot," the police officer said.
An as yet unidentified criminal pumped three bullets into Gribovsky at the moment he was shutting the garage door. The mine director died on the spot.
A passer-by found his body later the same evening.
Police have several versions of the murder, but none of them is connected with Gribovsky's work in the mine, the paper reported.
"It's also ruled out that he may have been linked with illegal explosives trade," Zhegulov told the paper. "He is known to have been involved in some kind of illegal business, but exactly what it was we have yet to find out."
Gribovsky's former boss, ex-director of oil shale company Eesti Polevkivi Vaino Viilup, characterized the murdered man as a good worker who never caused any problems.
"Gribovsky was one of the best industrial leaders. There's hardly been any better in Estonia," Viilup said.
Police suspicions of Gribovsky's links with shady business were a surprise to Viilup.
"Apart from being a former colleague of Gribovsky's, we also were neighbors and I for sure noticed nothing suspicious in his conduct and activities," he said.