That day, police moved on the 40-year-old's alleged killers. Raiding a house in the neighboring state of Kedah, they rescued 17 Rohingya migrants being held against their will, according to a statement by Penang police.
Eight alleged traffickers from Malaysia, Myanmar and Bangladesh were arrested.
The murder of Abul Kassim casts rare light on what Rohingya activists say is widespread abuse by human traffickers in Malaysia, who are willing to use extreme methods to protect their lucrative but illegal business.
Abul Kassim regularly supplied police with information on the activities of traffickers, said Abdul Hamid, president of the Kuala Lumpur-based Rohingya Society in Malaysia.
Since 2012, more than 100,000 stateless Rohingya Muslims have fled violence and poverty in Myanmar. Most travel in traffickers' boats to Thailand, where they are held by traffickers in squalid jungle camps before a ransom is paid.
Relatively wealthy Malaysia to the south is the destination for most Rohingya who flee. For some, it is far from safe.
Relatives and witnesses told Reuters of three abductions in Penang in 2013 and 2014, from a home, a coffee shop and the street. In addition, a Rohingya man was confined and tortured after being brought by traffickers through Thailand.
Three of the four cases ended in murder, they said.
Fortify Rights, a Southeast Asia-based rights group, documented another three suspected killings of Rohingya by traffickers last year.
Banned from legally working and fearful of police harassment, few victims bring their case to authorities. Those who do say police have taken little action.
Confirming cases is difficult. Local media give the issue little coverage and Penang state police did not respond to further questions about Abul Kassim's killing. National police spokeswoman Asmawati Ahmad did not reply to Reuters' questions on that case or other suspected Rohingya murders.
Interviewed by Reuters in late 2014, Penang police chief Abdul Rahim Hanafi denied traffickers had killed any Rohingya in the state that year.
"WE ARE NOT SAFE"
Police quoted in the local media said Abul Kassim's killing was likely to be connected to a money dispute.
A Kuala Lumpur-based Rohingya leader, who declined to be named for fear of retribution, said quantifying crimes was difficult due to the power and reach of traffickers in northern Malaysia.
"If we try to get information about the traffickers, they will simply target the person who tries to get information. We are not safe," he said.
Such cases include the alleged abduction and murder of Rohingya cousins Harun and Sayed Noor in 2013 and 2014, according to witnesses interviewed by Reuters.
Harun, 35, had his first run-in with traffickers in early 2013, when he was kidnapped from a Penang shop and held for a week for a ransom of 7,000 ringgit ($1,942), recalled his uncle, Mohammad Salim, 50.
After his release, Harun lodged a complaint with police and fled into hiding, Salim said.
In retaliation, traffickers took his cousin Sayed Noor, aged about 30, and held him as barter for Harun and 50,000 ringgit, Salim said. Several months later, Sayed turned up dead, his body showing signs of torture and mutilation.
In early 2014, the traffickers caught up with Harun.
Months later, his uncle, Salim, received a call from a Thai mobile number, telling him to leave town.
"The trafficker told me himself he had killed Harun."
A similarly chilling message was sent with the alleged murder last March of Sadek Akbar, 17, who had traveled from Myanmar with the help of traffickers.
After passing through a Thai camp and being ransomed for release, Sadek was imprisoned in a safehouse in Penang. Traffickers then demanded 2,000 ringgit for Sadek's release, his uncle, Altaf Hussain, told Reuters.
"We couldn't afford it, so they beat him to death and dropped him by the side of the road," Altaf, 48, told Reuters.
Altaf's account of retrieving the body from hospital was verified by another Rohingya witness and a Malaysian journalist, who both declined to be named.
"MILLIONS OF DOLLARS"
Hampering a full account of the problem is Malaysia's patchy record of protecting millions of migrants, including nearly 150,000 registered refugees and asylum seekers living there.
Relatives of victims are reluctant to report crimes to police, fearing months of detention for migration violations and shakedowns for bribes, according to Fortify Rights executive director Matthew Smith.
"There are millions of dollars being made through the trafficking of Rohingya. It's unsurprising that illicit profits of that magnitude would bring out violent behavior," he said.
The United Nations High Commissioner for Refugees (UNHCR) declined to comment on specific criminal cases, but has received "regular reports of abuse, intimidation and exploitation of Rohingya refugees," said spokeswoman Yante Ismail.
"Under Malaysian law, all refugees are treated as undocumented and illegal migrants, and there is no national system in place to provide them with protection."
(Additional reporting by Trinna Leong in George Town, Malaysia; Editing by Mike Collett-White)