Based on the statement taken from the 69-year-old female victim, the attack followed a simple pattern _ the suspect befriended the victim and offered to buy her food and drink, the victim then woke up in the hospital's emergency room missing her mobile phone and cash.
The case, which occurred on Oct 4, has angered Pol Maj Gen Thitirat Nongharnpitak, deputy chief of the Metropolitan Police Bureau, because it is the sixth of its kind to have been reported since January this year.
Four other victims of similar crimes include monks seeking treatment at the Priest Hospital across the street from Ramathibodi Hospital. Another incident was reported at Mo Chit bus terminal.
Pol Maj Gen Thitirat said there had also been similar cases at Phramongkutklao Hospital and Hua Lamphong train terminal, but the victims did not lodge complaints.
The deputy commissioner called a meeting with investigators from Metropolitan Police Division 1, Phaya Thai police station and Bang Sue police station to track down the attacker. Police believed all of the cases were related.
For the Ramathibodi case, the suspect was captured on security camera footage. He was wearing a long-sleeved shirt and jeans at the time of the assault. His nose and mouth were covered with a mask.
The surveillance camera footage showed that after he committed the crime, the suspect rode his motorcycle to a mall to buy pillows, pillow cases, a rice cooker and other necessities.
Pol Maj Gen Thitirat asked investigators to review similar cases to look for connections and was convinced the druggings and robberies were the work of the same individual or group of individuals.
"We reviewed similar cases to look for a connection. We learned who their targets are, where they operate, and that they prefer to strike shortly after payday," he said.
Pol Maj Gen Thitirat's major concerns about this case centred around the drug used on the victims. It has been identified as odourless and colourless Xylazine, generally used by veterinarians for sedating animals.
According to the commissioner, people are allowed to buy the drug without a doctor's prescription, even though it is classified as a dangerous medicine. There is a high risk of overdose and death, if wrongly administered.
After inspecting footage from several surveillance cameras, police identified the man from the Ramathibodi case as Somkiat Petchngam, 43, from Chachoengsao. An arrest warrant was issued for him on Oct 12, about a week after the most recent crime.
Police tracked him down to Khao Saming district in Trat where he was arrested on Friday.
Pol Maj Gen Thitirat said Mr Somkiat confessed to the charges.
He allegedly admitted to druggings and robberies in several areas including Noppawong, Bang Sue and Phaya Thai.
"I'm sorry," Mr Somkiat said to his victims who came to identify him at a press conference on Saturday. "I didn't mean to harm you. I thought the [Xylazine] drug is safe to use on humans."
Mr Somkiat said he bought the drug from Koh Chang in Trat province where he saw a veterinarian use it to sedate dogs.
He said he chose ageing women and monks for his victims as they were "easy targets".
On Saturday, at least three more victims showed up who suspected Mr Somkiat was responsible for drugging and robbing them. One of them was a 76-year-old patient, Pichit Yunaisil, who said he was drugged at Ramathibodi Hospital on Oct 4.
"I was at a canteen and put my water glass nearby. I remembered seeing a man sitting beside me and that was all I could remember. I woke up again in an emergency room and found my 1,000 baht bank note and ATM card missing," he said, adding that that robber also used his ATM card to withdraw 38,000 baht from his bank account.
Pol Maj Gen Thitirat called on authorities to do more to protect the public from harmful substances, saying the purchase of Xylazine should be regulated.
"Purchases of Xylazine should require a prescription from a registered vet. I think people have been exposed to dangers that could have been prevented," he said.
Following the incident, Surasak Lila-udomlipi, director of Ramathibodi Hospital, issued a circular letter asking hospital staff to keep an eye out for criminals.
A warning has been posted in the hospital's premises advising patients and their families not to accept food or water from strangers and not to leave their food and drink unattended.
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