Police in Udon Thani are busy investigating a strange case in which no one has been murdered and no valuables have been stolen. In fact, the two victims in this case are already dead.

It is alleged a monk robbed the victims' bodies from the grave to use in occult rituals. The monk and his disciples were arrested and are currently in police custody after officers pressed charges of "colluding to steal assets at night" against them. The monk was disrobed before being arrested.

The grave robbery became public during the Songkran festival when villagers in Ban Non Sa in Prachak Silapakhom district went to their village cemetery to make merit for the dead.

On April 12, Buali Chuwiang and Anong Hipkaew filed complaints with the police that the corpses of their daughter and son respectively, which were buried pending cremation, were missing.

The families of the deceased were shocked by the macabre theft and appealed to officers to quickly find the corpses so they could perform traditional northeastern burial ceremonies, said Pol Lt Col Chamlong Panchana, investigation inspector at Prachak Silapakhom police station.

One of the stolen corpses belongs to Sirirat Akkharat, 26, Ms Buali's daughter. She died while she was five months' pregnant and was buried with her baby at the cemetery in May last year.

Sirirat's corpse was found beheaded. The robber made off with her head, leaving behind her body and the baby. It is believed the head was to be used for a black magic ritual.

The other corpse belongs to Noppharat Hipkaew, 32, Ms Anong's son. The man was shot dead at a shrine in Kumphawapi district and his body was also buried at the cemetery late last year until its disappearance.

Pol Lt Col Chamlong's investigation team began a search for the robber. Villagers reported seeing strangers in their neighbourhood, including a monk who came to the village last month.

The monk immediately drew officers' suspicion because he is well-known for black magic and claiming to predict winning lottery ticket numbers, Pol Lt Col Chamlong said.

He allegedly uses corpses in his rituals, especially of those who died from unnatural causes.

Police searched the area for the suspect and eventually found him. Phra Eun Aphiyo, 65, is originally from Buri Ram. He entered the monkhood on May 12, 2013, at Wat Pha Thamma Charoen in Ban Muang Kao in Udon Thani's Kumphawapi district, according to investigators.

During the police's initial questioning, Phra Eun admitted locals asked him to give them winning lottery numbers while he stayed at Ban Phasuk Buddhist monastery in Kumphawapi district.

But as pressure from investigators mounted, police yesterday said the monk admitted he had colluded with two disciples to steal corpses at Ban Non Sa for use in black magic rituals. He used the corpses to divine lucky lottery numbers.

One of his disciples, Woraphong Senaphon, 20, reportedly confessed to police that he and Khunthong Khetnu, 32, helped Phra Eun dig up four corpses.

Mr Khunthong told police that he and Phra Eun discarded Sirirat's skull at Bua Daeng swamp in Kumphawapi district.

Pol Lt Col Chamlong believes the suspects are also behind the theft of another two corpses from a cemetery in Kumphawapi district in March. The corpses belong to two siblings, aged nine and eight, who died of drowning.

During the search of Phra Eun's sleeping quarters at Wat Pha Thamma Charoen, police seized items including a mahout's hook and a hammer.

Police are still searching for the missing corpses.