Can I be charged with a crime after the fact if no arrest was made at the time?

Two issues are at play - the first is the potential criminal charges that still could be filed. If they are in the middle of a big investigation and an incident occurs which could interfere, some times federal agents will initially walk away from an arrest. (An example is when there is a large drug investigation involving a lot of people going on and one car gets popped with drugs. They might not arrest those folks because they are trying not to scare the others into stopping their illegal activities.) Or, it could be that the prosecutors who handle those types of cases were not available to advise them so they gathered the evidence, took photographs, and let him go until they are able to consult with a prosecutor. Or, it could be that they are not going to file charges. I do not think he is out of the water yet, though. As far as the truck is concerned, when a vehicle is used for an illegal activity, even when they do not prosecute the criminal activity, they can still seek forfeiture of the vehicle. He will be served with forfeiture documents. He will need a lawyer to advise him on filing an answer because if he attempts to get the vehicle back, he will be subjected to answering discovery questions and requests for admissions, etc., in which truthful answers under oath might incriminate him.