The 42-year-old man, who is believed to be Irish, was arrested near his home in the resort of Mijas Costa, near Marbella on Spain's southern coast on Friday. The suspect's girlfriend and her mother were also being held over possible involvement in the serial slayings. Police suspect him of stabbing two prostitutes to death, the first in August and the second a month later. The killer was dubbed the "10 murderer" because both women were killed on the tenth of the month. The first woman, said to be 45 years old and of Argentine origin, was found dead in her apartment in the nearby resort of Calahonda. She had been stabbed at least 15 times and was found by her son with a pillowcase tied round her neck and a cushion over mouth. A month later police discovered the body of a 47-year-old Ecuadorian born woman at her home in San Pedro near Marbella. She had 12 stab wounds to her chest and neck. Both women reportedly advertised their services through local newspapers. Post mortem evidence suggested the two women shared the same killer. Police are investigating whether the suspect could be linked to other unsolved murders across Spain.