Ludo is a "person of interest" up until the time that Jackie is convicted.
Why? Because while the cops may believe him, they also believe that he may have information that will help to convict Jackie. What is not being said is that Ludo may not even know he has any such information. So he will be questioned over and over, hoping some small detail comes out that has yet to be revealed.
In standard interrogations, the story will be the same time after time. Yes, small differences in the telling are normal and accepted. What leads to concern is if the repetition is exactly the same, time after time. This means it has been rehearsed. That alone arouses suspicion.
This is pretty much standard in all police inquiries.