Almost seven months after mass graves believed to be of human trafficking victims were discovered at Wang Kelian in Perlis, Malaysian police have yet to arrest anyone.

Head of the special team probing the case SAC Goh Kok Liang said last month that six foreign suspects had been identified, but they are still at large today.

"No development, we are still tracking them down," he said when contacted here.

He admitted that police did not know whether the six - believed to be Thais and Myanmar - were still in the country.

Police announced in May the discovery of graves with 106 skeletal remains believed to be of Rohingyas, and 28 human trafficking camps.

PHOTO ALBUM: Rohingya graves: Six foreign suspects identified

The 139 graves, some of them empty, sat atop a hill hundreds of metres above sea level.

Thai police charged 88 people, including a general, with human trafficking last month.

The seeming lack of action on the Malaysian side has led to people asking why there were no Malaysians found to be involved when the human trafficking and murders took place on our side of the border.

"Our investigations so far have not revealed any Malaysian involvement ... but we are still investigating," said SAC Goh.

ACP Maszely Minhad, assistant director of D7C, the anti-trafficking in persons and smuggling of migrants unit in Bukit Aman, explained the problems Malaysian police faced.

"When the Thais raided the camps on their side, the victims and culprits were still there.

"When we went to the camps on our side of the border, all had left. So we had to depend on witnesses we found nearby," he said.