The average person rides a bicycle, and the body weight is on the rear wheel. But when going uphill, the cyclist must bend forward so that the center of gravity falls on the handlebars, so that the marks on the front and rear wheels are roughly the same. Now that both roads are uphill, the tyres of the murderer should be about the same depth as before and after. The traces on the right side of the road are exactly like this, so Chen Bo concluded that the murderer escaped from the right side of the road.