The word salvage for me is interesting because in the Philippines, it's an example of an autoantonym and it's opposite is probably more well-known than its regular definition.
Normally, salvage means to rescue something or to make the most out of a bad situation. I don't profess to know the entire history of how the Filipino term came about but I expect in the beginning, the English definition of salvage was being used. Its present definition started to pop up when dead bodies where frequently found in unexpected places like rivers or garbage dumps (which are places you'd expect to salvage material and goods that one can presumably still use). Many suspect that the dead bodies were the work of either criminal elements or vigilantes. The initial reports to the public probably used the correct terminology, referring to the discovery as "dead bodies were salvaged in location XX". However, the association between dead bodies and the word salvage would slowly work its way up to the Filipino psyche that instead of stating that entire phrase, to salvage someone conveyed the entire idea (we Filipinos love shortcuts!).
Currently, to use the word to salvage someone doesn't mean to rescue someone but rather to have them killed and supposedly dispose their body in an anonymous way.