The deceased and the four suspects who lived together were all international students, and they all came from different countries. If the deceased wants to leave a death message, the simplest thinking logic is to point out the murderer by specifying the nationality. The easiest way to distinguish nationality is the national flag. It is inferred that the victim died before he finished folding, and two folds were missing. The deceased may not know the flags of other countries, but the flag of his own country should be very clear, so according to the death information, it is inferred that the murderer is British, that is, A, the murderer.

This is a motorcycle helmet.

Make sure this is the correct answer, and check the information for a long time. This is a murder case on a whim, not on purpose.

The murder weapon must not be in the house, otherwise even if it is cleaned, blood can be found.

The deceased couldn't think of anything too complicated before his death.