Thinking Critically on a Crime Scene

Welcome, Expert Investigator! We need your help! A local apartment building has experienced a series of mysterious burglaries. In each case, the apartment door appears to have been kicked in$,$ but every time a loud noise was reported, the building security arrived too late to apprehend the thief. Tenants are suspicious that the thief lives in the building or is on the maintenance team.

What's the first step in solving this case?