A 51-year-old man was beaten to death with a hammer and his mother, 80, seriously injured at their Orihuela City home early on Tuesday morning.
The Policia Nacional have arrested a male suspect and discovered the murder weapon.
The attacker said he was owed €50 for doing some handywork.
When the occupants refused to pay him, he returned with a hammer to collect his debt.
Neighbours called the police at around 1.15 am after hearing a woman screaming.
A passing motorcyclist asked an Orihuela Policia Local patrol further down the road for help.
The vicious attack happened on Calle San Antonio de Padua.
Officers found the 80-year-old woman had suffered a severe blow to her head.
Her deceased son had been struck with an object.
The woman was taken to the Vega Baja Hospital in Orihuela before being transferred to the Elche General Hospital.
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