While capture by Israel is likely to be easily confirmed, establishing that a Hamas leader is (a) deceased (b) as a result of an action taken by the state of Israel, I will consult assessments and statements given by (1) Hamas, (2) IDF/Israel (3) intelligence services of other states such as the US, France, UK, etc.; as well as reporting by established media outlets such as the New York Times, Wall Street Journal, CNN, BBC, etc.