A spokeswoman for the local ambulance service in Spain told AFP on Saturday that an attacker killed a man in his forties and a woman in her seventies along with the boy, who was aged about 10 to 12, in the south of the city of Valencia.
"They died at the scene of the attack," while the two others, a woman of 48 with wounds to the chest and abodomen, and a man of 44 with wounds in his back and head, were taken to hospitals, the spokeswoman added.
Spanish news agencies said police arrested a man of 33 who was caught nearby covered in blood and is suspected of being the killer. Valencia police spokespeople were not available on Saturday to provide details.
Media reports said the attacker had gone round ringing on the doors to his victims' apartments before stabbing them, but no motive was cited.
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