David Daube, Studies in Biblical Law
For it was this rule which his brothers, by analogy, applied to their case, though, needless to mention, they abused it. Having sold Joseph to the Ishmaelites, they died his coat red and delivered it to Jacob as the only trace left of his child, just as a shepherd would submit to his master the last few scraps of an animal killed by a wild beast….
In point of fact, the law underlying their procedure appears to have been, if not identical with Exodus 22:12, at least couched in remarkably similar language. For Jacob, when forced to admit to his sons that a wild beast has caused Joseph’s death, uses the same emphatic form that we find in that provision.