A car thief stole a car but he did not know that the car belonged to Sherlock Holmes. When the fact was known to Holmes, he started investigating the case and as we know how good he is at that, four suspects were arrested soon. All four of them were seen near his car at the time when it was stolen.
He asked his partner Dr. Watson to examine the four suspects as he was busy in some other case. Dr. Watson used a newly invented lie detector while taking statements from the suspects. Each suspect gave three statements which are mentioned below:
Suspect A:
1. "In high school, I was in the same class as suspect C."
2. "Suspect B has no driving license."
3. "The thief didn't know that it was the car of the chief of police."
Suspect B:
1. "Suspect C is the guilty one."
2. "Suspect A is not guilty."
3. "I never sat behind the wheel of a car."
Suspect C:
1. "I never met suspect A until today."
2. "Suspect B is innocent."
3. "Suspect D is the guilty one."
Suspect D:
1. "Suspect C is innocent."
2. "I didn't do it."
3. "Suspect A is the guilty one."
At the end of it, Dr. Watson became confused by so many contradicting statements made by the suspects. The lie detector also malfunctioned and it could just tell that out of all the 12 statements made, only 4 were true. He then told all the details to Sherlock who found the car thief within moments.
Can you find out who the car thief is?
Solution:
In total, five statements have been made in which nothing has been revealed by the possible culprit and they are A1, A2, A3, B3, and C1.
If you look closely at the statements A1 and C1, they are contradictory but that is not just it. It is clear that at most one of these statements can be true if both are not false.
Nothing much can be explained from the statements A2 and B3. But it is doubtful that A2 would be false and B3 would be true at the same time.
A3 is true as followed from the introduction.
Let us now focus on the remaining statements and see how many of them are true.
Statement B1
A is the thief: False
B is the thief: False
C is the thief: True
D is the thief: False
None of them is the thief: False
Statement B2
A is the thief: False
B is the thief: True
C is the thief: True
D is the thief: True
None of them is the thief: True
Statement C2
A is the thief: True
B is the thief: False
C is the thief: True
D is the thief: True
None of them is the thief: True
Statement C3
A is the thief: False
B is the thief: False
C is the thief: False
D is the thief: True
None of them is the thief: False
Statement D1
A is the thief: True
B is the thief: True
C is the thief: False
D is the thief: True
None of them is the thief: True
Statement D2
A is the thief: True
B is the thief: True
C is the thief: True
D is the thief: False
None of them is the thief: True
Statement D3
A is the thief: True
B is the thief: False
C is the thief: False
D is the thief: False
None of them is the thief: False
Now in total of all the statements
A is the thief: 4 True, 3 False
B is the thief: 3 True, 4 False
C is the thief: 4 True, 3 False
D is the thief: 4 True, 3 False
None of them is the thief: 4 True, 3 False
Now if we combine the results with the fact that A3 is correct, the results will change as
A is the thief: 5 True, 3 False
B is the thief: 4 True, 4 False
C is the thief: 5 True, 3 False
D is the thief: 5 True, 3 False
None of them is the thief: 5 True, 3 False
Now we know that only four statements can be true from all the twelve (the lie detector told us that). Thus statements A1, B2, B3 and C1 must be false in that case which means that Suspect B is the car thief.