A day before the massacre, the Thai press reported on a play staged by student protesters the previous day, which allegedly featured the mock hanging of Crown Prince Vajiralongkorn. In response to this rumored outrage, military and police as well as paramilitary forces surrounded the university.
The 14 October 1973 uprising overthrew the unpopular Thanom regime and saw him flee Thailand together with General Praphas Charusathien and General Narong Kittikachorn, collectively known as the "three tyrants".[1]:209 Growing unrest and instability from 1973 to 1976, as well as the fear of communism from neighboring countries spreading to Thailand and threatening the interests of the monarchy and the military, convinced the latter to bring former leaders Thanom and Praphas back to Thailand to control the situation. In response to Praphas's return on 17 August, thousands of students demonstrated at Thammasat University for four days until a clash with Red Gaur and Nawaphon toughs left four dead.[1]:233 On 19 September, Thanom returned to Thailand and headed straight from the airport to Wat Bowonniwet Vihara, where he was ordained as a monk in a private ceremony. Massive anti-Thanom protests broke out as the government faced an internal crisis after Prime Minister Seni Pramoj's attempt to tender his resignation was rejected by the Thai Parliament. On 25 September, in Nakhon Pathom, west of Bangkok, two activists putting up anti-Thanom posters were beaten to death and hung from a wall, an outrage that was soon established to be the work of Thai police.[1]:235 A dramatization of this hanging was staged by student protesters at Thammasat University on 4 October. Deliberately or unfortunately, the student at the end of the garrote bore a resemblance to Crown Prince Vajiralongkorn.[1]:235 The following day, as Seni struggled to put together his cabinet, the newspaper Dao Siam published a photograph of the mock hanging on its front page.[2]:90 With the tacit approval of King Bhumibol, announcers on army-controlled radio stations accused the student protesters of lèse-majesté and mobilized the king's paramilitary forces, the Village Scouts, Nawaphon, and Red Gaurs to "kill the communists".[1]:235 At dusk on 5 October, some 4,000 people from these paramilitary forces as well as military and police personnel gathered outside Thammasat University where student protesters had been protesting for weeks. This set the scene for the Thammasat University massacre the following day