This statement of yours is not supported by the stats you quoted. The question in the YouGov stats was whether it was okay to be happy someone was dead after the assassination, not whether the shooting was justified. Those are very different matters.
The YouGov polling does ask that question though and states the following -
Because the story doesn't publish the statistical significance of the difference between the groups, it's impossible to tell whether these alleged differences between/among the groups is meaningful or just noise in the data.