A total of 88 people, including four crew members, were rescued. A man and a woman died in the incident. The boat was carrying undocumented migrants heading for neighboring Malaysia through an unguarded route when it sank on Saturday morning.

Tanjung Balai Asahan Navy base commander Lt. Col. Aan Sebayang said that most of the victims were rescued by fishermen; he said that the crews of at least three fishing boats were involved in the rescue.

“These fishermen were initially hesitant in helping because they were afraid of being implicated in illegal human trafficking, but they decided to help anyway,” Aan told The Jakarta Post on Monday.

The officer said the boat sank as a result of a leak, not because it was hit by heavy seas as previously reported.

The incident was the latest in string of fatal boat accidents involving undocumented migrants departing for Malaysia.

It takes around three to four hours by boat to reach Malaysia from the coast of North Sumatra.

Last month, the Navy intercepted 34 undocumented workers trying to leave for Malaysia on a motorboat from Batu Bara regency also in North Sumatra. 

In January, in a different part of the province, Labuhanbatu Police thwarted an attempt to transport 54 undocumented workers heading for Malaysia. The workers came from all over the archipelago and had paid smugglers between Rp 300,000 (US$20) and Rp 4.5 million to get them to Malaysia. 

Late last year, two boats carrying undocumented workers sank in Malaysian waters. Both had departed from Batu Bara. In the first incident, 21 people died when the boat sank off the coast of Johor Baru on Dec. 15. In the second, 10 people died and 35 were rescued off Sekinchan in Selangor on Christmas Day, while the rest remain missing.