The cases offered by Dr Matz are not cases of double effect. They are of a genre often presented to challenge the notion that there can be an absolute moral prohibition on euthanasia. Generally, the point of such cases is to suggest that in some circumstances, death is so inevitable, so imminent, and the pain that will precede death so unbearable, that the only morally appropriate response is to end the life of the person by active means.
Space does not permit a full response to such challenges. However, it is useful to note that the cases presented by Matz have 2 morally important features that are not typically part of the stock counterexamples. First, the harm to be done to the victim is not caused by an act of nature or an ongoing process already set in motion by a human act, but by an intervening agent's potential evil act in the future. Therefore, in these cases, to kill the victim oneself is to collaborate in evil—to do the evil deed for the killers—albeit with more compassion.