Without some sort of visual examination, this is purely a guess but there is a pine sawyer beetle that vectors a  pine wood nematode which causes pine wilt disease. The beetles feed on the tree and lay their eggs in the tree but the nematodes enter the vascular system of the tree and effectively plug it up so the tree may die pretty quickly. The tree seems to die from the crown down. As the beetles leave the trunk, you may find BB sized holes in the trunk which may provide a clue to their existence. The nematodes are microscopic in size and are internal so you wouldn't see them and the nematodes hitch a ride on the beetles as the beetles hatch and ride to another tree. A sample could be sent for confirmation but be certain to talk to your Ag agent regarding the type of sample needed. There are many other fungal, bacterial and insect problems that can infect Scotch pine trees. With pine wilt disease, you may lose all the trees because trying to control the disease may be cost prohibitive. Contact an arborist for info on control if this is the problem.