The 22-year-old was set to join City from Parma in the January but the deal did not go through as the midfielder was refused a work permit.
Mancini then tipped off his former club Inter Milan, who signed the Kenya international.
“Manchester City were very interested in Mariga but they had problems and we know it thanks to Roberto Mancini,” said Oriali.
“He called us because the Home Office denied the transfer of the player.
“Then we threw ourselves at once to close the deal with the player as soon as possible.
“We are all very happy, the rating is part of all: the club, the chairman and the coach.”
