The teen student who stabbed and killed another boy at school on Monday claimed the victim had been demanding money and assaulting him over the past two weeks, police say.
The stabbing occurred at Narknarwaouptump School on Pattanakan 26 Road in Suan Luang district at about 8.35am on Monday when students were being dismissed from their morning assembly.
Pol Col Wachirakorn Wongboon, chief of the Khlongtan police station, said that during an interrogation that also involved teachers and the mother of the slain boy, the 14-year-old attacker said he had often extorted 20 baht from him at lunch breaks.
Both boys were of the same age but studied in different classrooms.
The alleged extortionist usually claimed he needed money to buy cigarettes, Pol Col Wachirakorn said, and allegedly also punched the head and face of the other student.
"The boy had been treated this way three or four over the past two weeks. Having the grudge, he bought a knife and took it to school this morning," Pol Col Wachirakorn said.
Police had yet to verify the claim by asking witnesses if they had seen such behaviour, the station chief said.
He confirmed that the attacker appeared to be mentally stable and answered police questions clearly. A psychologist who observed the interrogation concluded that the boy seemed mentally normal. However, police would bring the boy for a mental health test, Pol Col Wachirakorn said.
This contradicted the earlier speculation that the attacker might be a boy with special needs.
Police did not find any trace of drug abuse in the urine of the suspect, who admitted to smoking cannabis once in September last year, the station chief said.