I don't believe a Sasquatch (provided they exist, of course) needs to be killed to prove anything. I don't believe one should be captured or otherwise inconvenienced, either. I know that the current paradigm is that "science demands a body" but, to me, that is "science's" problem. Once there is enough "proof" that they DO exist (and I believe that DNA should be enough), I believe there will be more people/organizations that are much better equipped (resources) out looking for them. Once an individual/family group is located, I believe that a simple study should be enough. Over time, I would think that a body would become available for science to play with thru a natural course.
If Sasquatch exist, I don't think they need any protection, either. All I would ask is that we recognize their existence, study them so that we are able to determine their needs, take those needs into consideration when any decisions are made that could affect them or their habitat...and leave them alone. They have obviously survived without our "protection" and, if left alone, will continue to do so.