Why is that sperm tails are lost before the heads? Also do heads last longer than other forensically significant proteins?

it's because the tails are not needed as long as the head. The tail contains the molecular machinery to produce energy for the time the sperm is motile. Once it has reached the egg it is no longer required so is degraded. Source (https://www.askmehelpdesk.com/biology/sperm-tails-sperm-heads-475.html)

Tails are more fragile and are made of proteins which bacteria attacks first [1 (http://projects.nfstc.org/bsw/presentations/03_BioScreening_Semen_012010_CBS_JMS.pdf)]