March 23 every year is observed as Shaheed Diwas to mark the death anniversary of Indian freedom fighters Bhagat Singh, Shivaram Rajguru and Sukhdev Thapar. 

In 1928, Bhagat Singh plotted to kill a police officer to avenge Lala Lajpat Rai's death. 

Rai, who led a non-violent protest against the Simon Commission, had succumbed to injuries sustained during a lathi charge ordered by British police officer James A Scott. 

Following this, Singh, Rajguru and Sukhdev planned to execute Scott. Singh had publicly declared to execute Scott. However, the trio mistook British police officer John Saunders for Scott and allegedly fatally shot him. Following the shootout, Singh continued his freedom struggle. Meanwhile, the Britishers charged the three freedom fighters for Saunders' killing.  Later, in 1929, Bhagat Singh and his associates dropped two bombs at the Central Legislative Assembly in Delhi and allowed themselves to be arrested, while shouting the famous freedom struggle slogan, "Inquilab Zindabad", or "Long live the revolution".

It was on March 23, 1931, when the three were hanged to death in the Lahore Central Jail in British India (now Pakistan) by Britishers.  Every year March 23 is observed as Shaheed Diwas or Martyrs' Day.