Help the detective record the witness's exact statement about the clumsy thief.

"I watched the thief ___ the diamond and put it in his pocket," the witness testified.

The correct answer is take.

Verbs of perception (like watch, see, hear) are followed by an object and a bare infinitive (the base verb without "to") when you witness the entire completed action.

While the -ing form (taking) can sometimes be used for actions in progress, it doesn't work here because the second action is a bare infinitive ("and put it in his pocket"). The verbs must match!