On this day, April 3 ...

1996: The "Unabomber" Theodore Kaczynski is arrested at his remote Montana cabin for a series of bombs that killed three Americans and injured 24 more over a 17-year period.

Also on this day:

1860: The legendary Pony Express begins carrying mail between St. Joseph, Mo., and Sacramento, Calif. (The delivery system would last only 18 months before giving way to the transcontinental telegraph.)

The legendary Pony Express begins carrying mail between St. Joseph, Mo., and Sacramento, Calif. (The delivery system would last only 18 months before giving way to the transcontinental telegraph.) 1882: Jesse James is shot to death in St. Joseph, Mo., by Robert Ford, a member of James’ gang.

Jesse James is shot to death in St. Joseph, Mo., by Robert Ford, a member of James’ gang. 1936: Bruno Hauptmann is electrocuted in Trenton, N.J., for the kidnap-murder of Charles Lindbergh Jr.

Bruno Hauptmann is electrocuted in Trenton, N.J., for the kidnap-murder of Charles Lindbergh Jr. 1944: The U.S. Supreme Court, in Smith v. Allwright, strikes down a Democratic Party of Texas rule that allows only white voters to participate in Democratic primaries.

The U.S. Supreme Court, in Smith v. Allwright, strikes down a Democratic Party of Texas rule that allows only white voters to participate in Democratic primaries. 1948: President Harry S. Truman signs the Marshall Plan, which is designed to help European allies rebuild after World War II and resist communism.

President Harry S. Truman signs the Marshall Plan, which is designed to help European allies rebuild after World War II and resist communism. 1965: The United States launches the SNAP-10A nuclear power system into Earth orbit; it is the first nuclear reactor sent into space.

1968: Martin Luther King Jr. delivers what turned out to be his final speech, telling a rally of striking sanitation workers in Memphis, Tenn., that “I’ve been to the mountaintop” and “seen the Promised Land. I may not get there with you. But I want you to know tonight that we, as a people, will get to the Promised Land!”

1968: North Vietnam agrees to meet with U.S. representatives to set up preliminary peace talks.

North Vietnam agrees to meet with U.S. representatives to set up preliminary peace talks. 1974: Deadly tornadoes begin hitting wide parts of the South and Midwest before jumping across the border into Canada; more than 300 fatalities result from what would become known as the “Super Outbreak.”

Deadly tornadoes begin hitting wide parts of the South and Midwest before jumping across the border into Canada; more than 300 fatalities result from what would become known as the “Super Outbreak.” 1996: An Air Force jetliner carrying Commerce Secretary Ron Brown and American business executives crashes in Croatia, killing all 35 people aboard.

An Air Force jetliner carrying Commerce Secretary Ron Brown and American business executives crashes in Croatia, killing all 35 people aboard. 2003: Atlantic magazine editor Michael Kelly, 46, becomes the first American journalist to be killed while covering the Iraq War.

Atlantic magazine editor Michael Kelly, 46, becomes the first American journalist to be killed while covering the Iraq War. 2009: Tom Braden, who helped launch CNN’s “Crossfire” and whose memoir “Eight is Enough” inspired a TV show, dies in Denver at age 92.

2014: David Letterman announces during a taping of the “Late Show” on CBS that he is retiring as host in 2015 (Stephen Colbert would be named as his replacement a week later).