Miranda rights: Can Holmes's statements to police be used against him?

James Holmes's lawyers are arguing over whether his statements to police "It's just me," can be used against him. He was questioned by police shortly after the shooting in Aurora, CO, in July 2012, where's he's alleged to have shot theater goers at a movie showing.

Article here. 

It was two hours later that Holmes was read his Miranda rights, which would have alerted him to the fact that statements could be used against him.

My take on this is that the prosecution will argue that a public safety exception applied, since they were wondering if another shooter was present.The broader issue is when does Miranda rights apply? Generally, Miranda rights apply when you are in police custody, or custodial interrogation. So if a suspect isn't in custody, would Miranda apply?

The defense attorneys admit that this is a side issue, however, because they're not denying he was shooting in the theater. Instead, their defense will involve whether the defendant was sane at the time of the shootings or not.