You have been assigned as the Forensic Auditor of ABC Co. to assist in the investigation of a missing file from the company's premises containing trade secrets.
During investigation, you find out that on the day of the incident three employees entered the room where the file was being held.
While interviewing the three employees, you are informed that one of them is truthful while the remaining two are liars. This is what they tell you:
Employee 1: I entered the room first or second. File was not present when I left.
Employee 2: I entered the room second or third. File was present when I left. None of us stole the file.
Employee 3: I entered the room third. File was present when I left.
Which of the employees stole the file?
The file was stolen by the second employee.
First we need to identify the liars. Employee 2 is a liar since he claimed that none of them stole the file. Employee 3 is a liar because he claims that the file was present when he left which is not possible if he entered the room last. As employees 2 and 3 are liars, this also implies that employee 1 is truthful.
However, looking at statement of employee 1 alone, we cannot conclude who the culprit is. In order to make any sense of the statements of employees 2 and 3, we will have to reverse them to know the truth. This is how their statements would look like if we reverse them:
Employee 2: I entered the room first. File was not present when I left. Someone from among us stole the file.
Employee 3: I entered the room first or second. File was not present when I left.
It is clear from above that employee 2 was the first one and that is when the file went missing. Employee 3 and employee 1 only entered the room later when the file was already gone.