Thais paid their respects with flowers and prayers on Tuesday to the victims of a 1976 massacre of pro-democracy students by state forces, an event given new resonance by a recent surge in student-led protests.
As people laid wreaths at the Thammasat University monument, 64-year-old survivor Wichian Visutanakon recalled the bloodshed.
"The worst thing is those people who did those crimes are still proud and don't regret their actions," he said.
On Oct. 6, 1976, security forces attacked some 2,000 student protesters on the campus, accusing them of being communist sympathisers and seeking to bring down the monarchy. Dozens were killed - shot, hanged or beaten to death.
The events have never been investigated officially.
This year's memorial ceremony drew more younger sympathisers than in recent years after nearly three months of street protests against the government, in which some protesters had called for reforms to curb the powers of King Maha Vajiralongkorn.
A 23-year-old student, Thantara Sriserm, said she was worried the protests might be violent like 1976, but that "it might be less likely as these days we have smartphones that we can use to film and share things quickly".
The protests are the biggest challenge in years to a ruling establishment long dominated by the army and the palace. The next big protest is set for Oct. 14.
Protesters seek the removal of Prime Minister Prayuth Chan-ocha, a former junta leader whose critics accuse him of keeping power by manipulating 2019 elections. He says the vote was fair.
Last month, tens of thousands of protesters gathered just outside Thammasat University also cheered calls for palace reform, breaching a longstanding taboo on criticising the monarchy. Protests have been peaceful so far.
Government spokesman Anucha Burapachaisri said the Oct. 6 memorial ceremonies happen every year and the government has no objection to this year's event.
The #Oct6 hashtag in Thai was among the top trending on Twitter in Thailand, used more than 410,000 times.
"I hope that instigating hatred in the name of love for the nation, religion and monarchy, as seen in the Oct. 6 incident, will not happen again," said opposition MP Rangsiman Rome, a former student activist.
Thailand became a constitutional monarchy when absolute monarchy ended in 1932. Thailand's army has seized power 13 times since then and has on several occasions carried out bloody crackdowns on protesters.