Present participle; the ongoing process of describing or proving something through specific details and relevant circumstances.
From circumstantiate + -ing suffix. Present participle form showing the action in progress. Built on circumstance (Latin circum- + stare).
Investigators are circumstantiating a theory by gathering all the details around it—the timeline, the locations, the relationships. It's the detective process of surrounding a conclusion with enough evidence that it becomes hard to doubt.
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