MEXICO CITY—Prosecutors in Mexico City say they are searching a multiplex theater to find clues in the strange case of a boy shot to death inside a movie.

The city prosecutors' office says the boy's father heard a whistling sound, then noticed his son slumped over and convulsing in the next seat.

The theater chain and the prosecutors' office said Monday that neither the staff nor the father immediately appeared to realize the boy had been shot in the head.

He was taken to a hospital after the Nov. 2 shooting and died Nov. 4. Local media say he was 10.

Prosecutors say the investigation began once they were advised the case involved a probable homicide.

Mexico City has largely been spared the drug violence affecting other parts of the country.