Few things are more chilling than the discovery of an unmarked mass grave.
It speaks of the darkness and callousness that reside in the hearts of some who walk among us. So low is their regard for fellow men that they have no qualms about throwing bodies into pits in obscure locations so as to hide wrongdoings.
More often than not, these cold-blooded people are directly responsible for the deaths of the unfortunate victims.
We usually associate mass graves with war crimes, but we must now wrap our heads around the fact that such graves have recently been found in Songkhla province in southern Thailand, along with abandoned "slave camps", and they have nothing to do with any armed conflict.
Instead, they are horrific offshoots of the human trafficking trade, which is a crime too.
The Thai authorities believe that the remains are of illegal immigrants from Myanmar and Bangladesh who have died from illness or abuse.
They were among the thousands, including Rohingya asylum seekers, who are said to arrive in Thailand by boat every year.
Many of them head to Malaysia, making stops in jungle camps with terrible conditions. They are often at the mercy of syndicates that care little for the people they are bringing across borders.
According to the United Nations Office on Drugs and Crime, thousands of people have lost their lives as a result of the indifferent or even deliberate actions of migrant smugglers.
The shocking developments in Thailand raise questions about Malaysia's role in the fight against human trafficking.
There is plenty of anecdotal evidence that the human trafficking networks operate in Malaysia as well.
That is logical, of course. The flow of human traffic has to be managed all the way from the source countries to the destinations.
It is telling that the US State Department's 2014 Trafficking in Persons Report, issued last June, reclassified Malaysia as a Tier 3 country after four years on the Tier 2 Watch List.
The report describes Malaysia as a "destination and, to a lesser extent, a source and transit country for men, women, and children subjected to forced labour and women and children subjected to sex trafficking". Thailand is in Tier 3 as well.
There have been allegations that Malaysia also has these so-called slave camps, but the Kedah police chief has denied it.
Even so, the smuggling of people into Malaysia from Thailand is not only the latter's problem.
We have the Anti-Trafficking in Persons and Anti-Smuggling of Migrants Act, which covers the many aspects of human trafficking.
The criminals have to be stopped, and because of the cross-border nature of their activities, a country acting alone will not fare well against them.
It has to be a multilateral effort, and it is encouraging that Thailand is calling for talks with Malaysia and Myanmar to address the region's human trafficking trade.
At the same time, Malaysia needs to examine what else it can do at home to be more effective in countering human trafficking. Perhaps it should start by weeding out any complicity, incompetence or apathy among public officials.