Ligature material in case of hanging is kept preserved as -

Ligature is cut away from the knot. Depth, width, direction, raised edges of skin, zones of hyperaemia, presence of duplicate strangulation marks, dried excoriations due to slippage of the implement, textile weave pattern, distribution of petechia in skin, scratch marks All these things are to be noted at the ligature site, after the ligature is cut away. Ref: K.S.Narayan Reddy's Synopsis of Forensic Medicine and Toxicology, 29th edition, Chapter 13, page-177.