Why does Mr Utterson feel he needs to break down the door?

Inside Jekyll's home, Utterson sees that all the servants have, "huddled together like a flock of sheep." Clearly, Poole is not alone in his concern, and one maid breaks down into sobs. Utterson and Poole approach Jekyll's cabinet door in the laboratory, and Poole announces that Utterson is asking to see Dr. Jekyll. A voice that does not sound like Jekyll calls out to say that he will not see anyone. Utterson agrees that something must be amiss. Poole then reveals that he has seen the person hiding in Jekyll's room, a "creature". Utterson realizes he has no choice but to solve this mystery once and for all. He and Poole fetch an ax from the surgery room to break down the cabinet door.