Why do the soldiers question whether Ellen is really a Johansen?

A few hours later, three German officers pound on the front door. Annemarie cracks open her bedroom door and watches as he talks to her parents. The German officer knows that the Johansens are friends with the Rosens, and therefore, he thinks that Mama and Papa must know where the Rosens are. Mama and Papa insist that they have no idea. The officer rudely demands to search the house and starts toward Annemarie’s bedroom, despite Mama's pleas to him not to wake the children.

Annemarie realizes that Ellen is still wearing her gold Star of David necklace. She panics and instructs Ellen to take it off, but Ellen has never removed it before and cannot undo the clasp. Desperate, Annemarie rips the necklace off Ellen's neck and crumples it in her hand moments before the officers barge into the room. When the officers as the girls to identify themselves, Ellen introduces herself as Lise. The head officer, however, notices that Ellen has dark hair, unlike the rest of the family. He asks why, and Papa quickly tears some photos from the family photo album. One of the photos is of Lise, who had dark hair as an infant. The officers finally accept Papa’s explanation and leave the apartment.