Help the dramatic detective review the facts with his prime suspect. Choose the correct question forms to complete the dialogue.

Detective: "Let's review your statement. You said Jimmy took the necklace. So, who stole the necklace? Jimmy did!"

Suspect: "Yes! And then I immediately phoned my mother!"

Detective: "Ah, but who did you call before that? The security guard!"

So, who stole the necklace?

When "who" is the subject of the sentence (the person doing the action), we do not use an auxiliary verb like "did". We just use the main verb in the past tense.

Ah, but who did you call before that?

When "who" is the object of the sentence (the person receiving the action), we use standard question word order with an auxiliary verb (Wh-word + auxiliary + subject + verb).