Stubborn police wrote off the death of Nanthawan (above) as "natural illness" and it took a Facebook campaign to get them to solve the brutal killing. (Bangkok Post photo)

Were it not for the determination of her sister to see justice done, the murder of Nanthawan Wichaigun in Surat Thani eight months ago might have gone unsolved after local police concluded she had died from an illness.

On Dec 8 last year, the student at Suratthani Rajabhat University’s International School of Tourism was found lying near her motorcycle by a deserted road off a main street near the Si Surat bridge in Muang district. She was barely alive and foaming at the mouth, and died on the way to hospital.

Local police initially believed Nanthawan, 21, died of a natural illness. They discounted the robbery theory, as she was still wearing a golden necklace and ring, although her mobile phone and handbag were missing. Police concluded there was no evidence of foul play.

But the girl’s elder sister Natthanari, 25, refused to believe it. She knew her sister would never have travelled to such a desolate spot alone. Her dogged determination persuaded police to review the case, which led to the arrest of a woman last Wednesday for Nanthawan's murder.

Ms Natthanari said she knew early on her sister's death was suspicious. If her sister had suddenly fallen ill, where was her mobile phone, handbag and motorcycle keys? Why were there bruises on her neck and wrist? And why was her hair and some of her clothing wet?

On Dec 15, she petitioned the Muang district police chief to re-examine the case. But police found no new clues and insisted Nanthawan had died from an illness. They argued that after falling ill, she probably lost consciousness and fell near a river, which accounted for the wet clothes and hair.

Ms Natthanari remained doubtful and sent a petition letter to the Provincial Police Region 8 commander. But it was a Facebook post which she wrote on Jan 31 that made the difference.

Posting under the headline “Waiting without hope”, she wrote about her fight to get a review of her sister's case. The post attracted a large following and a chorus of public voices calling on police to dig deeper into the girl's death.

On Feb 11, Nanthawan’s relatives were informed of an autopsy result from Surat Thani hospital which said the girl was suspected to have drowned as experts found bacteria which live in water in her lungs. For the family, this was a clear indication she might have been murdered.

However, local police told the family they still believed Nanthawan died of an illness, perhaps a side-effect of her taking diet pills. They offered no evidence to support this theory. They also said an opportunist robber could have found her sick at the scene and taken her missing belongings.

But they could not explain why she had supposedly driven to the desolate spot. “Crimes often occur in that area,” Ms Natthanari told the officers. “It’s impossible my sister went there.”

She filed a complaint asking the Crime Suppression Division to look into the case. A joint investigation team was set up and the trail led to a fortune teller, Anchali Ramatchit, 29 — the last known person to have seen Nanthawan.

Ms Anchali had earlier been treated as a witness, but police felt her account did not help their investigation. She then left Surat Thani soon afterwards. Police became suspicious and discovered she had been seen near the scene where Nanthawan was found. They tracked her down in Phichit and arrested her last Wednesday, and she allegedly confessed to the murder.

Pol Lt Gen Decha Butnamphet, chief of Provincial Police Region 8, said Ms Anchali admitted taking the girl to the river to perform a rite to rid her of bad fortune. She duped Nanthawan out of 30,000 baht and was afraid she might later complain and demand her money back. When the victim became thirsty, Ms Anchali allegedly gave her water laced with acid and Nanthawan collapsed into a convulsion after drinking it.

After the confession, Surat Thani police denied ignoring Ms Natthanari's requests to review the case. It just took them "a little time" because they had to do their work carefully, the officers said.