I'm going to 180 here. Based on the details of the case, as presented in the
appeals court decision, there was reason to check. The victim lied about how he got hurt and based on the presence of blood, it was not unreasonable to want to check a locked room.
The appeals court sets the threshold as needing to know that there is someone in need. They feel this was addressed when they find the victim and then the person who attacked him. The attacked victim did not indicate multiple victims, therefore the police don't have an objective reason for suspecting any one else is in danger. However, the victim clearly lied about the circumstances of the injuries, so the fact he doesn't indicate multiple victims is, in my mind, not as relevant.
If there was a victim in the locked room, and that person died because the Police had not checked... that would have been viewed as a terrible error in judgment.