Complex sentence: In captitivity, however, there have been about two dozen non-fatal and three fatal incidents on humans since the 1970s, specifically perpetrated by just two (possibly three) killer whales, all who where known to eachother.
Split into simpler sentences: In captitivity, however, there have been about two dozen non-fatal on humans since the 1970s. There have been only three fatal incidents, all perpetrated by just two (possibly three) killer whales, all who where known to eachother.