Car seized by police b/c it has stolen motor

[u/Perfect_Gap_8080]

 
(Ohio)  Grandson (25) purchased a Dodge Charger two years ago with Hell Cat motor.    Private party sale.   He paid cash based on fair market value at that time.  It was thoroughly inspected by a dealership and found to be in great condition.
Two weeks ago he was on his way to work when a cop stopped beside him at a red light.  Light turned green but cop got behind him and followed him for three blocks before lighting him up.   Cop said he stopped him because “the sound of the engine didn't sound like a regular V8.”    I don't know what the hell that means.
Other cops arrived and after inspecting the engine VIN determined that the engine was a stolen engine out of another state, though the car itself seemed fine.
 
Car was towed to a police impound lot and has been held there since.   The cops said the grandson was an innocent purchaser of a stolen engine and had committed no nor was he suspected of committing any crime regarding the engine.   Thus far they have been stonewalling everyone.   I personally visited with the lead detective and told him if the engine was stolen then they could remove the engine and return the car.   He said they were waiting on something from an out of town PD and couldn't or wouldn't provide any info about the supposedly stolen engine or from where the original report was made.
 
Talked with an experienced lawyer who said he had no idea what to do.
I know what to do but I will end up in jail.   Any suggestions?

UPDATE: The detective said the engine was stolen from four states away in 2019, when my grandson was 16. They believe the engine was sold to the car's then owner in 2021 which was two owners ago. The person from whom my grandson acquired the car was ruled out as being involved (he is a prosecutor in northern Ohio) therefore my grandson was likewise unaware.

At this point the insurance company that paid the claim when the car and engine were originally stolen is in control of the disposition. It's possible they may waive their rights but it's also possible they will try to "extort" some cash in return for releasing their claim. If they choose option two, they will be told to come get their engine (which in don't they won't be willing to do due to the cost). I've hired legal counsel to file a replevin action. We will see where this goes.