It happened at a US base in February, at the height of Turkey’s Afrin invasion, when Kurdish disappointment with the US abandonment was high. The exact location of the base is not given in the article. The Task and Purpose article alleges that wounded civilians heading there, “mostly of women and children, were turned away by the SDF because they were not Kurdish”. US Marines Cameron Halkovich and Kane Downey get the wounded in the base for treatment against alleged SDF objections.
Later in the night, Halkovich and Downey go out to visit another Marine on sentry duty. An SDF fighter guarding the gate is not there. Halkovich pauses to take a leak while Downey walks on. Downey hears two AK-47 shots, looks backs and sees “a lone SDF soldier, standing over Halkovich with a rifle”. Downey shoots dead the SDF while Halkovich survives the shots in the leg.