The midfielder left Chelsea for Toro last month.
"I’m very happy to have arrived, to be here, and I can’t wait to get started,” Casadei told Toro TV.
“This isn’t the first year I’ve tried to come back to Italy. Torino have always shown interest, so I’ve always pushed to come here. When I found out there was a possibility this summer, I didn’t hesitate, so I’m very happy.
“The first rumours were already a couple of years ago, even before I went to Chelsea, there was already interest from Torino.
“Then things turned out differently, but thanks to the president, I was able to come here. I’m really very happy.
“It was the right time to return to Italy. I had been trying to come back for a while, but things didn’t go as I wanted, in a way. I really wanted to return to Italy, and now I’m finally here.”