The first interview was with the head of the institution. He mainly inquired about my background and skills, and then explained the institute's current and future projects.
For the second interview, he invited one of his group leaders whose research best matched my skills and background. This time we had more scientific and detailed discussions. In the end, they said they thought I had a good chance of getting an offer.
At the third interview, I received an offer, but I had to decline due to my personal situation.