I've been a Police Officer in Virginia for 18 years, and during that time have worked thousands of vehicle crashes, most of which fortunately, have not involved motorcyclists. I would like to explain the process the officer undertakes while working a crash. Crash is a different word from accident. 99% of all incidences where a vehicle strikes another vehicle or looses control and wrecks are the result of driver error. I have only worked one crash in 18 years that was truly an accident. This was a dynamic front tire deflation that caused the vehicle to run off the road, and this could be argued that the driver lacked the skills to maintain control.
First and foremost, we are concerned for any injured party. The absolute first thing I ask everyone, is if they are injured and need medical care.
I then look for all of the parties involved, and any impartial witnesses. (An impartial witness would not be your buddy who was in your car, or riding with you. It would be the pedestrian on the corner, or another motorist.) If witnesses are present, I prefer to speak to them before I speak to the involved vehicle drivers. The point of speaking to the witnesses and the drivers is to gain as complete a picture of the events leading to the crash as possible. In addition I look at the scene for physical evidence (road condition, skid marks, debris, vehicle damage, ect). If you decide to heed the advice of Mr. McGrath and refuse to speak to the police, I may not be able to gain a complete picture of the crash.
After I gather the information from witnesses, drivers, and the scene I complete the state mandated crash report. This report is one of the first things an insurance company will ask to see. As a police officer I must determine, as best as the evidence allows, who I feel is at fault. If I determine a violation of law has occurred I will charge that individual.
Mr. McGrath's reasoning behind the statement refusal is "At the scene of an accident (crash), your adrenaline is pumping, you may be in pain, and you may be angry," all of which may be true. But I have found through years of very high stress encounters, the best time to remember what occurred is as soon after the event as possible. It saddens me that our society has become so fraught with people and insurance companies unwilling to accept their responsibility that we now have a lawyer advising motorists not to speak to the police. This is a bit of editorializing but I feel this is the result of years of lawyers and insurance companies doing what ever they can to not accept responsibility or pay for their clients mistake.
Mr. McGrath's advice is absolutely lawful. You do not have to speak to the police if you choose not to. It may, however, cause vital information to be lost and not properly considered during the investigation.
In conclusion I strongly encourage all motorists (motorcyclists especially) to educate and train themselves continually. Hone your riding/driving skills and mentally prepare yourself for that crash, even if it never happens.