Ern raised an eyebrow at Michael's behaviour. While he did portray Michael's anger rather well, he was still uncertain with regards to the actual facts of the matter. He needed to be sure before he could even fathom setting the guy loose. He wasn't one to take any chances, especially if they were suspecting a highly dangerous killer in the vicinity.
"She's your girlfriend, Corner? I didn't know that," he said, affirming his answer and searching his mind for a few questions to ascertain his identity. "Where were you on the evening of November 7th? And November 8th?"