It will just take time for your panther to get used to his new surroundings, and to you.
Try to just leave him alone, give him his private space.
Try hand feeding using a silkie, or something he likes.
Put the feeder in you hand. With your fingers together, hold it up to him about 6'' away, and hold very still.
If he backs ways, slowly pull your hand out and try again later.
If he sits there, and does not try to hide or get away from you thats a good thing.
If he is watching you and not the bug on your hand, that means he doesnt quite trust you yet.
If he is looking at the bug, and not you, thats a good sign, even if he doesnt take the feeder, just sits there, staring at it.
If he does that, gently place the feeder on a branch in front of him so he sees it and back away.
Every time you open the cage, even to clean, you should have a treat for him, no matter if he takes it from you or not.
He will slowly learn to associate you with food.
I recommend not letting them out of their cage to free range until they are trusting enough to take food from your hand, and not run and hide when you open the cage door.
If his other owner had him tame, it should not take long to get him to trust you as well, since he is already used to humans.
Work with him every day, open his cage, do the hand feeding thing, just stand there and let him see that you are not aggressive.
Once he starts taking food from your hand regularly, you can start moving closer to him untill you are almost touching him.
Baby steps, patience, persistance, move slowly.
You want to get to the point where you can gently slide your hand under him and have him climb into it.
It's best to keep him up higher then your eye level, and they dont like to be stared at. He may be more likely to take the bug from your hand if you turn your head and look away.
He may start by just putting one foot on your hand, then 2, then all 4.
I'm sure he will come around for you, just be patient and gentle