Seems like an OK definition of primary vs. secondary sources (which itself is kind of academic; what you're really looking for is reliability).

The part to me is "here's a video of them in Hamas captivity, here's a still of them dead from a block away, this totally means Hamas killed them (despite an abundance of violence in a tiny area, with a background of indiscriminate Israeli bombing)." Anyone drawing a conclusion about who killed them is working off their priors.