The man, identified as Muhamad Usen, aged about 30, was taken from the Immigration facility in Sadao, where he was being held, to Had Yai Hospital on March 18.
He died the next day, the source said. On Wednesday, his body was handed over to local Muslims for burial. It is believed he came from the troubled township of Sittwe, in Burma.
The man was not recorded as a Rohingya, but as a ''Burmese Muslim.'' This bureaucratic lie is an indication that Thai authorities now support the Burmese Government's racist contention that Rohingya do not exist as a separate ethnic group.
Another source told Phuketwan that the man's death was related to untreated injuries inflicted by people-traffickers while he was being held in a secret camp near the Thai-Malaysia border.
According to the source, several other men with severe injuries from traffickers are being held in Sadao Immigration. They have yet to be seen by a doctor, the source said.
More deaths in custody are feared. Hundreds of Rohingya men are being held in overcrowded conditions at Immigration centres around Thailand.
Conditions are reported to be especially bad for 270 men confined in an overcrowded space at Phang Nga Immigration centre, north of Phuket.
The men are among about 1700 Rohingya who were either ''rescued'' from smugglers' camps or arrived in Thailand on flimsy boats in January.
About 300 women and children are part of the groups and are being held in slightly better conditions at family welfare refuges.
However, at least six boys are known to have fled from a family centre in Phang Nga, north of Phuket - probably with the help of local people-traffickers.
Thailand's Government has undertaken to hold the Rohingya for up to six months to assess their status and determine their futures, working with the United Nations High Commissioner for Refugees and NGOs.
Reports relayed from the captive Rohingya indicate they are growing increasingly frustrated as the weeks pass. Their aim remains to travel on from Thailand to Malaysia, where some have family or friends waiting.
Three boatloads of Rohingya are reported to have arrived in Malaysia in the past 10 days.
Record numbers of Rohingya have been ''helped on'' towards Malaysia since October by the Thai military as Burmese authorities continue to tacitly support ethnic cleansing by local Buddhists in Rakhine state.