Photographing Jack Ruby shooting Lee Harvey Oswald
25 November 2013 Last updated at 01:37 GMT
On 24 November 1963 - two days after US President John F Kennedy was killed - the man arrested on suspicion of carrying out the assassination was himself shot dead.
The image of Jack Ruby firing a pistol at Lee Harvey Oswald is one of the most famous of the 20th Century. It was taken by Dallas Times-Herald photographer Bob Jackson and won him the Pulitzer Prize.
Now living in Denver, Colorado, he spoke to the BBC about taking the shot of a lifetime - and explained why being a split-second slower than a competitor made all the difference.
Produced by Markus Zeffler, Charly Jaffe and Amir Payam
First Person is a series of video features published every Monday on the BBC News website which tell the stories of unique individuals from all walks of life in their own words.