On the night of October 12th, the ”Sunburst Medallion” was stolen from the highly secured display case in the city museum. The theft occurred sometime between the museum closing at 10:00 PM and the night guard, Mr. Hemant, completing his final round at 1:00 AM. Three primary suspects were identified, all of whom had recently been dismissed from their museum positions: Anjali, the former curator; Bharat, the former security expert; and Chitra, the former exhibits designer.
Here are the established facts and their alibis:
• The security system logs show that the display case was opened using a specific five-digit code, which only Anjali and the museum director (who was out of the country) knew.
• Bharat’s alibi is that he was at a distant relative’s birthday party from 8:00 PM to 1:30 AM. Multiple independent witnesses confirmed his presence throughout the entire period.
• Chitra’s alibi is that she was working late at a downtown graphic design studio. A timestamped security camera from the studio’s entrance shows her entering at 7:00 PM and exiting at 11:45 PM. The studio is a 20-minute drive from the museum.
• Mr. Hemant, the night guard, stated he checked the medallion at 10:30 PM, and it was still there.
• Further investigation revealed that a small, distinctive silver button was found near the display case. Anjali is known to frequently wear a coat with similar unique silver buttons. The security expert, Bharat, had previously boasted that he could remotely disable a
certain type of magnetic lock-the same type used on the medallion’s case-without needing the code, though the log suggests the code was used. (269 words)

Assessing Necessary Conditions
What condition is necessary for Chitra to have stolen the medallion?

Correct Answer: The theft must have occurred after she left the studio and before 1 am

To determine which condition is strictly necessary for Chitra to be the thief, let us analyze the established timeline and facts from the problem statement:

1. Chitra's Location: A timestamped security camera confirms Chitra was at the graphic design studio from 7:00 PM until 11:45 PM. Therefore, she was physically unable to be at the museum to commit the theft prior to 11:45 PM.
2. Time Frame of the Crime: The museum closed at 10:00 PM, and the night guard completed his final round at 1:00 AM, by which time the theft was discovered or completed.
3. Necessary Logical Condition: For Chitra to have stolen the medallion herself, she must have been at the museum during the time of the theft. Since she was verifiably at the studio until 11:45 PM, the theft could only have been committed by her if it occurred after she left the studio (at 11:45 PM) and before 1:00 AM.

Let us evaluate why the other options are not strictly necessary or correct based on the text:
• "She must know the five digit code" – Not necessarily required, as lock-tampering or other security bypass methods (or acquiring help) could theoretically occur, whereas physical presence at the scene during the theft window is an absolute requirement.
• "She must have left the graphic design studio before 11.45 pm" – The security camera confirms she left at exactly 11:45 PM. Leaving prior to 11:45 PM contradicts the verified evidence.
• "She must have worked with Anjali to disable the locks" – This is speculative and not a established mandatory condition for her physical capability to commit the theft.

Thus, the necessary condition for Chitra to have stolen the medallion is that the theft must have occurred after she left the studio and before 1 am.