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I am sorry to learn of this situation. Unfortunately I believe I understand what the situation is and why your attorney advised you in the way that they did.
When you file bankruptcy, civil claims (such as a claim for "conversion" (the civil equivalent of theft)) become the property of the bankruptcy estate (they no longer belong to you as an individual). So you no longer have the right to prosecute these cases, the trustee may, or may not, decide to prosecute these cases belonging to the bankruptcy estate.
I also can see where your attorney would see potential issues with prosecuting a case to recover an asset that would immediately be liquidated. (Let's say you (or the trustee) were successful in litigating against this individual and got the bus returned (or a cash judgment), that bus, or the cash, would immediately be paid to your creditors as part of the bankruptcy distribution.
Unfortunately, at this point you are going to have a very difficult time resurrecting any type of claim against this individual - the claim belongs to the bankruptcy estate (in whatever form you choose to shape it as), and the defendant only needs to raise this issue with the court to have your case dismissed. You can of course speak to your bankruptcy attorney to discuss the matter and see if there is any possibility that the bankruptcy attorney "abandoned" the claim, but this would be very rare.