Colombian police have arrested a man suspected of murdering 29 children found in two ditches in the city of Pereira. Pedro Pablo Ramirez was arrested on Wednesday December 30, 1998, in a suburb of Pereira, 300km (200 miles) east of Bogota, in connection with the murders. The childrens' bodies - many missing body parts and showing signs of torture - were found in two separate graves in the city last month. The first, found on 12 November, was discovered when a boy walking through an overgrown lot saw a skull in the bushes. He alerted authorities who dug up the lot, finding incomplete skeletons but 13 skulls. River-bed grave The second discovery was made less than a week later in a river-bed below a city highway. Searchers investigated a ravine after workers fixing electrical lines spotted what they believed were animal bones. Forensic experts believe the eldest of the victims was 16, and at least half were under 10 years old, according to State Prosecutor Elena Orsorio. Investigators have linked Mr Ramirez to the killings of at least three children in Pereira and possibly three other children there and in the nearby town of Armenia. Murder cases re-opened Police are re-opening the cases of 80 child murders in recent years in the two cities. Mr Ramirez had previously been in prison for sexual crimes, according to Pablo Elias Gonzalez, who heads the investigation being conducted by the Colombian attorney-general's office. Police have still not come up with a motive, although rumours of satanical rituals have been circulating after minors came forward saying they had been abused in such rites. But authorities are considering other motives including "social cleansing", organ trafficking and a paedophile serial killer. Due to the state of decomposition - particularly of the bodies in the first find - indentification has been difficult. Parents and relatives with children missing have beseiged police stations and officials for information of their lost loved ones.