Walter decided now was not the time for a locked door to get in the way of a little child and whomever it was taking care of it. He consoled Sarah to stay a touch closer to avoid the zombies as he didn't wish her or Bella to be attacked whilst they were dealing with this and there no time for the subtle approach. They might be attacked or paralyzed with fear but it didn't matter because if they wanted to be saved they needed to open the door now! Crowbar in hand he jams it it tight and says<strong>"Stand back from the door! And you two cover me! Sarah and Bella go in first when this door breaks!"</strong>Then Walter would exert force in a hard attempt to force the door open, locked or not.