Equipment missing and found at construction site

Considering this situation, you are a project manager for the construction project. As far as you know so far the project is progressing ahead of the schedule and it is also below the budget. You have a very good relationship with your subordinate such as carpenter, plumbers, electricians and machine operator.

One day you decide to go to the site and found out that several pieces of valuable equipment are missing from the storage shed. When you start work again in the Monday you would discuss this issue with a supervisor and you realized that the missing equipment is back in the shed. What should you do? Why

Put a lock on the shed and give the key to one person with instructions not to loan out the equipment for personal projects.