Unfortunately, the MNA reported to be a witness of the US Marines incident, (Mumtaz Alam Gillani, National Assembly Member PPP), is not backing up the report, and is even threatening to sue Ansar Abbasi (the journalist who published this report quoting unknown eyewitnesses), if he does not debunk his article soon.
(remove blank spaces before n after each dot in these links)
thenews . jang . com . pk/top_story_detail.asp?Id=17453
www . app . com . pk/en_/index.php?option=com_content&task=view&id=53599&Itemid=2
paktribune . com/news/index.shtml?205998
pakistanpressfoundation . org/userMediaFilesDetails.asp?uid=14505
it's even on his Wiki page:
en . wikipedia . org/wiki/Syed_Mumtaz_Alam_Gillani
The report might still be true, but maybe the MNA is not backing it up personally to avoid trouble for himself.