Before Premadasa Sirima killed more youths in her office time due to the JVP revolts.
On April 5, 1971 early morning, due to some confusion, the police stations at Wellawaya and Moneragala in Uva province were attacked. But later, the attack was launched as planned on the same day, but in the evening. Accordingly, police stations at Badulla, Kandy, Moneragala, Amparai and Nuwera Eliya were attacked. JVP cadres - in groups of 25 to 30 - assaulted police stations in those administrative districts, using home-made weapons. Nearly 93 of the total of 273 police stations in the country fell to the insurgents. The government also evacuated many more police stations located in the most vulnerable areas. Almost the entire area of the south and west of Ceylon fell into the hands of the JVP and it was rumored that a JVP garrison was on the move to capture Colombo, the capital city.
On April 5 during the night, Srimavo Bandaranaike had hid under her office table, as Temple Trees had received a false alarm that the JVP had managed to cross parliament building and were marching on the Galle Road, on their way to the Temple Trees, to arrest the prime minister. Felix Dias Bandaranaike had arrived at midnight and the prime minister and others left for Colombo harbor to spend the night on a ship anchored there.
The JVP had planned to take into custody Mrs. Sirimavo Bandaranaike on the night of April 6th 1971. This task had been entrusted to JVP activist Piyasiri who was to have been assisted by Raja Nimal, an H. S. C. student of Sri Sangharajah Maha Vidyalaya, Maradana. Piyasiri's instructions to Nimal were that his group "should attack the residence of the Prime Minister, capture her and bring her dead or alive to Campbell Park that night". Fortunately, the Government received prior information of the plan and curfew was declared forthwith, thwarting the sinister plan of the JVP
On April 9th (Good Friday) Dr. Rex de Costa, a respected medical practitioner of Deniyaya was shot dead by JVP in the presence of his wife for treating injured constables and assisting them to carry out their duties in face of the JVP attacks.
The Army Commander, Major General Sepala Attyagalle, sent detachments under Lieutinent-Colonel Cyril Ranatunge to Kegalle. Brigadier P D Ramanayake directed operations from Galle, up to Sinha Raja forest, which reportedly sheltered the rebel headquarters. Under Colonel E D T Z Abeysekera an armed detachment was sent to North Central Province.
According to available official figures, at least 5,000, probably many more, died in the insurrection. According to unofficial figures nearly 25,000 Sinhalese youths could have been killed. Accounts from reliable sources indicate that many of suspected insurgents were summarily shot by a panic-stricken police and their bodies burnt on pyres consisting of old rubber tyres impregnated with diesel oil, thereby preventing any kind of identification.The police who had killed suspected or active insurgents, let the bodies float downstream in order to terrorise the people. Wijeweera in a statement from prison in 1972, had stated that 15,000 revolutionaries had been killed, but twice that number of innocent people had also died.
Throughout the months of June to October, the government was involved with the mopping-up operations. During those days it was reported that atrocities had been committed on a large scale. Summary executions were widely reported to have taken place, but the government denied all these allegations.
On July 20, 1971, Srimavo Bandaranaike told the parliament that a special investigation unit has been set up, "The task of this unit is to go into each of these [sic] 14,000 cases and to categorize them according to the degree of involvement of these persons and to release those, who in the opinion of the investigators need not be detained any longer."