Hiya! If this came with a short story or article I would have loved to se wit so I could better answer this question. However using process of elimination I don’t think it’s “was”, however “are”, “were” and “were not” depend on the story.
“Are” : the interviews are happening in present tense, they haven’t happened yet or they are in the middle of them.
“Were”: The interviews happened in past tense, they’ve already finished the interviews,
“Were not”: The interviews already happened and they were not meant to determine the cause of the accident.
Hope this helps!