Even investigators with years of experience under their belts can fall into the trap of false assumptions. Pol Lt Col Pitsanu Puangprom, deputy superintendent of Krabi provincial police station, knows this only too well.
Last week when Pol Lt Col Pitsanu led an investigation into the murder of local businessman Prasit Charungnoo, all the initial theories proved to be a fallacy.
The 51-year-old victim was an influential person shot dead on his way home in Krabi's Ao Luk district last Tuesday. His body was found near his vehicle, parked just 200 metres away from his house.
Prasit was the president of the provincial Palm Plantation Cooperatives and the village head for Moo 5 in tambon Kiriwong, Plai Phraya district.
Due to his controversial background as the cooperatives' manager, and a local political figure, the investigation began with the assumption his death resulted from a conflict in the cooperatives, said Pol Lt Col Pitsanu.
Authorities had launched a probe into corruption in the cooperatives and someone close to those circles had accused Prasit of being involved, he said. Police also suspected Prasit had enemies, as he carried a gun while travelling. But an inspection of the crime scene steered the investigation in a new direction, said Pol Lt Col Pitsanu.
Pol Lt Col Pitsanu: Lesson learnt.
Prasit must have been shot while standing outside his car, as no intelligent man would step outside his car if he saw his enemy waiting for him, said Pol Lt Col Pitsanu. He was shot three times, in the chest, rib, and finger.
The investigators knew they were on the right track when two witnesses later tipped them off. The first said he witnessed a pickup truck with a broken window parked on the side of the road 15km from the crime scene. Pieces of window glass were also found. The other witness had changed the pickup truck's flat tyre, and provided its licence plate number as evidence.
When police traced the plate number, it led them to Pol Sen Sgt Maj Bunlue Phetkho, 41, from Border Patrol Police 426, now recovering from shooting injuries at a private hospital in Phuket.
Police say Pol Sen Sgt Maj Bunlue admitted shooting Prasit in a fit of rage when Prasit passed him on the road "recklessly" as the policeman was driving to see his wife in Surat Thani last Tuesday.
Both drivers got out of their cars and argued violently, Pol Sen Sgt Maj Bunlue told police. The fight escalated until Prasit opened fire on him with a handgun, hitting him in the stomach and shoulder. He later sought treatment for those injuries in hospital. The shots also ruptured the tyre of his truck.
Pol Sen Sgt Maj Bunlue shot back, and said he did not realise he had killed Prasit. He drove 15km away, where the tyre was fixed by a private rescue team, who later became witnesses in the case.
In a similar case, Farut Thaiseth, the son of Chada, a Chartthaipattana MP for Uthai Thani, was gunned down in a drive-by shooting in Pak Chong district of Nakhon Ratchasima province in 2012. Police believed the motive was linked to politics until Mun Poonsub, 40, from Ratchaburi, turned himself in to police and confessed to shooting Farut over street-car racing.
"Things always go above and beyond our expectations. Police believed the motives for the shootings were related to politics. But the actual causes were just personal conflicts," Pol Lt Col Pitsanu said.
Lesson learned, he said. Investigators should stick to the evidence at a crime scene to identify suspects instead of relying on assumptions, which may prove groundless.