Sometimes it can take several months before the lab results come back from the crime lab. Your son needs to consult with a DWI lawyer as soon as possible so that he will be prepared in the event that he is arrested. It is imperative that your son not provide any further information or evidence to the government without the presence of his lawyer.
Brad is absolutely right. You need to start interviewing dwi attorneys right away. It may take some time, but your son could have some very real problems. When the labs do come back you can expect the police to arrest your son if they think alcohol or drugs played a part in the accident. In that event, you will need to have an attorney ready to handle bond hearings and evidentiary hearings very quickly. The defense of this matter will be very expensive so start preparing finances in case the worst happens. I would be happy to discuss the case more fully or you could call Brad. I can without hesitation tell you he is a very qualified dwi attorney.