The murder occurred around 5am at Wat Suwanpakdi in tambon Thakum, Muang district, said Pol Capt Kanthaphon Sakkhaprom, a duty-officer at Muang police station.
Phra Khru Kittisarakosol was lying dead on the monks' dais in the pavilion where prayers are offered when police arrived.
The abbot, 60, had three gunshot wounds, one in the stomach and two in the head.
About 60 horrified devotees were milling around in tears over the loss of the abbot.
Thammarit Jullasin, 56, spokesman for the temple who witnessed the attack, said a lone man carrying a pack of milk entered the pavilion and walked toward the abbot as if about to make an offering. Instead, he pulled out a gun and fired at the abbot in full view of people attending morning prayer. The gunman then left.
Police arrested Pinit Siriroop, 61, at his home in Muang district around 6am. He was taken Muang police station for interrogation.
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