In cases of death due to hanging, fractures of the thyroid cartilage, the hyoid bone, fracture of the cricoid cartilage, facial congestion, visible hematomas of the soft tissue, cartilage and bones of the neck, injuries to the sternocleidomastoid muscles, common carotid stenosis, venous obstruction, leading to cerebral stagnation, hypoxia, and unconsciousness, which allows muscle tone relaxation and final arterial and airway obstruction, arterial spasm due to carotid pressure, leading to low cerebral blood flow and collapse, vagal collapse, caused by pressure to the carotid sinuses and increased parasympathetic tone.
These are all the possibilities I can find. They do not have to all be present to prove death by strangulation from hanging, but these are all the signs they would look for.