Rigor mortis

mild temperatures

sets in about 3-4 hours after clinical death

full rigor for 12 hours

subsiding to relaxation at about 36 hours

after each power stroke of muscle contraction, you need ATP to recock the myosin head

so I think that if you have a bunch of cross bridges formed, and no ATP to detach the myosin, then you have rigor mortis

from wikipedia on rigor mortis

myosin molecules devoid of ATP become permanently adhered to actin filaments

form actomyosin complex

causes muscles to become rigid

release of autolytic enzymes stored in lysosomes takes place when pH becomes 5.5

these enzymes act at the myofibrillar proteins and hydrolyse them

breaks down actoymyosin complex

resolution of rigor