Tanzania national police chief Simon Sirro told the press conference that Dewji had already provided some information about the kidnapping.
"Mohammed Dewji told us that the kidnappers wanted money but were very afraid, even though they were armed. He asked them several times how much they wanted but they gave no figure," Sirro said.
Dewji did not know who his abductors were but believes they were from South Africa, his office told Forbes Africa
He also gave his captors contacts for his parents but they feared that they would be caught if they approached them, Sirro said, adding that they had finally decided to give up.
"We now know their network, we know in which country the plans were made," he said, without giving details.
Dar es Salaam police chief Lazaro Mambosasa meanwhile told journalists that Mohammed Dewji had indicated to him that his abductors spoke a southern Africa language, confirming suspicions that the kidnappers were foreigners.
Africa's youngest billionaire, Mohammed Dewji, 43, heads the MeTL Group which operates in about 10 countries with interests in agriculture to insurance, transport, logistics and the food industry.
He was born in Tanzania and studied at Georgetown University in the United States. He also served as a member of parliament from 2005 to 2015.
In 2013, he became the first Tanzanian to grace the cover of Forbes magazine and was named Forbes Africa Person of the Year in 2015.
Mohammed Dewji is also the main shareholder in Tanzania's Simba FC football club.
According to Forbes he is 17th on the list of Africa's billionaires, and worth $1.5 billion (1.29 billion euros).
He is married with three children. In 2016 he signed a pledge to donate at least half of his fortune to philanthropic causes, according to Forbes.