Convinced that an insurrection was brewing, British Brigadier General Reginald Dyer ordered that there were to be no public gatherings in Punjab, India. However, many citizens of India didn’t hear that announcement and on April 13, 1919, a peaceful protest congregated in the Jallianwala Bagh gardens.

Dyer mobilized his men and marched them to the gardens, blocking off one of the entrances. Dyer then ordered them to open fire, gunning down 200-300 unarmed civilians (a proper body count was never determined) while firing some 1,650 rounds over the course of about 10 minutes.

Dyer received some public criticism, but many in the British upper class lauded him for protecting the British Empire. The Hunter Commission which later made an inquiry into the slaughter held no one accountable. The Jallianwala Bagh massacre, also referred to as the Amritsar massacre, was a major turning point which helped spark Mahatma Gandhi’s civil disobedience campaign.

As legend has it, there was one survivor amongst the dozens of dead Sikhs in Jallianwala Bagh gardens. He was a young boy named Udham Singh. Brigadier Dyer died of a stroke in 1927, so the British lieutenant governor of Punjab, Sir Michael Francis O’Dwyer who had endorsed the massacre, became the young Sikh’s target.

Anita Anand is the author of a new book about Singh. In The Patient Assassin: A True Tale of Massacre, Revenge, and India’s Quest for Independence, she describes him as a patient assassin, one that sought the skills he needed to exact his revenge from wherever he could obtain them. In an interview for Crime Reads, Anand said:

He used the early immigrant communities in America and Britain for subsistence, support, and intelligence (convincing them they were the most important people in his life). Udham also sought teachers of greater standing, following the old adage “my enemy’s enemy is my friend.” He looked for any who hated the British Raj as much as he did.

Travelling to Africa, Udham met anti-colonialists while working on the British owned railways, or so-called ‘Lunatic Line.’ They taught him how to travel on forged papers and pass through international borders unseen. Next, America taught him how to walk with a straight back, speak English with confidence, act like he belonged. He learned how to merge into the shadows, procure weapons and plug into reserves of ‘black money,’ largely thanks to his association with a clandestine network of Ghadars—violent Indian nationalists operating out of San Francisco.

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In Russia and Eastern Europe, Udham came into contact with Bolsheviks, hell-bent on upending the old-world order. The Russians trained men like Udham happily, winding them up like a regiment of clockwork soldiers only to set them loose on the British Empire.

Ideology was no obstacle in his mission. Udham also travelled to Nazi Germany, where members of Hitler’s elite were battling the Führer’s ideas of Aryan racial superiority so that they could work with, fund, and support dissident Indians like Udham. He received all help with gratitude and added skills to his armory.”

In March 1940, O’Dwyer was due to speak to the East India Association in London. Singh quietly took a seat in the audience and waited. At the end of the meeting, Singh drew a revolver he had purchased in a pub and shot O’Dwyer in the chest, killing him instantly. Singh was arrested and put on trial. Upon his conviction he stated to the court:

I did it because I had a grudge against him. He deserved it. He was the real culprit. He wanted to crush the spirit of my people, so I have crushed him. For a full 21 years, I have been trying to wreak vengeance. I am happy that I have done the job. I am not scared of death. I am dying for my country. I have seen my people starving in India under the British rule. I have protested against this, it was my duty. What a greater honour could be bestowed on me than death for the sake of my motherland?”

Udham Singh is considered a national hero today in parts of India, with statues and monuments erected in his name. While Gandhi decried his act of revenge, others labeled him a freedom fighter. Initially, Singh’s remains were dumped into an unmarked grave. But under political pressure, they were returned to India where people came into the streets and threw flower petals over the procession.