Today is the 26th anniversary of the massacre of hundreds of pro-democracy student activists and other protesters in and around Tiananmen Square in the heart of Beijing – an event that Chinese authorities have erased from the official record.

Eleven Chinese university students living overseas are trying to jog their nation’s memory with a widely circulated letter. The effort began in Athens, Ga. From the Associated Press:

The letter remembers the government crackdown that killed hundreds and possibly thousands of unarmed protesters and onlookers. It demands that the Chinese leaders who gave the orders late on June 3 and in the early morning hours of June 4, 1989, be held responsible.

"We do not ask the (Chinese Communist Party) to redress the events of that spring as killers are not the ones we turn to to clear the names of the dead, but killers must be tried," the letter reads. "We do not forget, nor forgive, until justice is done and the ongoing persecution is halted."

An online copy of the document has reached readers in China with the help of software that let PDFs get past Chinese censors, Gu said. The document has already drawn a strong rebuke from the Communist Party-run Global Times, which said in an editorial that the students "harshly attacked the current Chinese regime, twisting the facts of 26 years ago with narratives of some overseas hostile forces."

Gu said he was addressing Chinese students who had not seen the troves of photos, film footage and eyewitness accounts about the massacre that he came across only after he left China to study.

"All they need to know is actually very simple," Gu said. "Some people died, and some people killed them. If you understand that, you don't have to understand a lot more."

In what's become an annual ritual, Chinese police were stepping up their vigilance in the capital Thursday to prevent any remembrance of the event. References to the massacre are nowhere to be found in Chinese media, and censors scrub social media posts that mention the event or its date.

In the only major act of commemoration in China, thousands of people in the semi-autonomous Chinese city of Hong Kong are scheduled to hold their annual candlelight vigil Thursday.

Gu said he was not worried how the letter would affect his chances of returning to his home country free from official harassment. He said his family had not run into any trouble yet from the authorities, although police had contacted the relatives of some of the co-signers.

"I can't do something always thinking about how this will affect me," Gu said. "Sometimes, it's just the right thing to do."