4 20: A spooky day for stoners and deadly attacks

The anniversary of the Columbine shooting, the Deepwater Horizon explosion, Hitler's birthday plus the day after the Waco Siege and the Oklahoma City bombing

For many people who smoke pot, April 20 is a day to gather and get high, but the day has seen more ominous and spooky events than just some stoners hanging out.

There are many explanations for why this day was chosen, some say it's police code for smoking in progress, the number of chemicals in marijuana and something to do with Bob Dylan songs.

The term '420' was started by a group of students at California's San Rafael High School in the late '70s, claimed a flyer passed out at a Grateful Dead concert. "It started as the police code for Marijuana Smoking in Progress. After local heads (Grateful Dead followers) heard of the police call, they started using the expression '420' when referring to the herb — 'Let's go 420, dude,'" reads the flyer. Although reports show police don't use that code.

Around 1990, High Times published the term and since then 4/20 has grown into a day to celebrate pot.

But April 20 isn't just a day for some to celebrate. Between April 19 and April 20, three large attacks, all within six years, have happened in the U.S. and left numerous people dead.

On April 19, 1993, The Waco siege ended leaving 76 people, including 20 children, dead. It began when the U.S. Bureau of Alcohol, Tobacco and Firearms tried to execute a search warrant of a compound near Waco, Texas, after hearing reports the Branch Davidian cult leader David Koresh was abusing children. Agents attempted to storm the compound and a gunfight ensued, lasting for two hours and leaving 10 dead. The ATF and FBI retreated and waited outside the compound while trying to negotiate with the cult. The standoff ended 51 days later on April 19 when an attempted raid resulted in the building going up in flames.

Only two years to the date after Waco, the largest terrorist attack in the U.S. other than 9/11 would take place. A bomb blast in a federal building shook all of Oklahoma city, killing 168 people and damaging 324 buildings. Forensic evidence quickly linked Timothy McVeigh and Terry Nichols to the blast. McVeigh, who was executed in 2001, is a militia movement sympathizer. It is said his hatred for the federal government and its handling of the Waco Siege made him carry out the attack.

And just four years and one day after the Oklahoma City blast, Columbine High School seniors Eric Harris and Dylan Klebold opened fire killing 12 students and one teacher before turning the guns on themselves in the Denver suburb. There is speculation the two were trying to plan their attack to coincide with Waco and Oklahoma City. Both shooters mentioned in videos that they hoped to outdo the previous events.

Columbine is the fourth deadliest school shooting in history. The second deadliest is the Virginia Tech massacre where Seung-Hui Cho shot and killed 32 people before committing suicide. It happened on April 16, 2007.

April 20 is also the anniversary of Korean Air Lines Flight 902 being shot down after it violated Soviet Union airspace. In 1978, the plane was able to make an emergency landing on a frozen lake, but two passengers died after a Soviet aircraft opened fire.

Most recently, in 2010, the Deepwater Horizon oil well exploded in the Gulf of Mexico killing 12 workers and beginning an oil spill that lasted six months.

The day is also Adolf Hitler's birthday.

(CP photo from Columbine school shooting)