A salesperson at a clothing store

You are a salesperson at a clothing store. You walk into the storage room to start ticketing some clothes that came in that morning and see a co-worker quickly take some pants from a box and put them into her knapsack. Your colleague does not see you enter the room. What do you do? Do you leave and say nothing to your employer? Do you say something to your colleague? Is your responsibility to your organization, your colleague, or both? What might be the implications of your decision?