corroborating evidence
陰惨な"処刑"が続いています。corroborating evidenceは，「裏付けの証拠，資料」という意味です。corroboratingには「処刑が真実であることを〕指し示す」というニュアンスがあります。（Inaho）
U.S. Believes ISIS Video Shows Beheaded American Hostage
The Islamic State released a video Sunday showing a black-clad executioner standing over the severed head of a man it identified as the American aid worker Peter Kassig.
Mr. Kassig, a former Army Ranger disappeared over a year ago at a checkpoint in northeastern Syria while delivering medical supplies.
In recent days, American intelligence agencies received strong indications that the Islamic State had killed Mr. Kassig. But without a body or other corroborating evidence, officials could not be certain.
But after the video was released and intelligence analysts were able to conduct an initial assessment, one senior American official said Sunday that the government was increasingly convinced that the video was authentic and that Mr. Kassig was dead.
