The fourth month of the year is generally pleasant, marked by beautiful spring days and the beginning of baseball season. April starts with our most whimsical day of the year, April Fool's Day, when friends pull harmless pranks on each other. But as the month progresses, the dates mark the anniversaries of illicit and sinister events and the fools of April are no longer funny.

Two dates in particular should stand out to law enforcement.

Domestic Terrorism

On April 19, 1993, federal agents assaulted the Branch Davidian ranch located about nine miles from Waco, Texas, ending a 51-day siege. The siege began when agents from the United States Bureau of Alcohol, Tobacco and Firearms (ATF) attempted to execute a search warrant at the ranch. The agents were met with gunfire and a battle ensued in which four agents and six Davidians lost their lives. After this incident, the Davidians retreated into their fortification.

As the Waco siege wore on, the FBI used a number of different tactics in an effort to secure a peaceful conclusion. These attempts were rebuffed by Branch Davidian leader/messiah David Koresh, who seemed to be preparing his group for a violent apocalypse.

Aware that conditions in the compound were deteriorating and that children were possibly being abused, U.S. Attorney General Janet Reno approved a plan to mount an assault on the compound. The FBI planned to puncture holes in the walls of the compound and pump in CS gas. The Davidians refused to exit the compound and instead intentionally set fires. With no chance to escape through the fires, 75 Davidians ultimately died by suffocation or after being shot by members of their own group.

As with any use-of-force incident, many were quick to criticize the actions taken by federal law enforcement agencies during the Waco incident. The debate rages to this day about the tactics used by both sides and what could have been done to avoid the loss of life. Much like Ruby Ridge—a 1992 shootout between federal officers and a family holed up in its secluded Idaho home—the Siege in Waco on April 19 has become a rallying point for those who oppose the United States government.

Two years to the day after Waco, on April 19, 1995, an attack against the U.S. government was launched in Oklahoma City. The bombing of the Alfred P. Murrah Federal Building by Timothy McVeigh claimed 168 lives and injured more than 800 others. Prior to 9/11, it was the deadliest terrorist attack on U.S. soil.

McVeigh's murderous actions were motivated by his hatred of the U.S. government, which started when he was in the U.S. Army and read "The Turner Diaries" (a fictional account of a modern day revolt by white supremacists against the government). His hatred intensified through the passage of the Brady Bill and the government's actions at Ruby Ridge and Waco.

It has been reported that when he placed the bombs he was carrying an envelope full of anti-government literature. These items included pages from The Turner Diaries and a bumper sticker that read, "When the government fears the people, there is liberty. When the people fear the government, there is tyranny." On this bumper sticker McVeigh had written, "Maybe now, there will be liberty!" McVeigh was wearing a T-shirt with the motto of the State of Virginia, Sic semper tyrannis ("Thus ever to tyrants"), which was shouted by John Wilkes Booth immediately after the assassination of Abraham Lincoln. His shirt also bore this quote from Thomas Jefferson: "The tree of liberty must be refreshed time to time with the blood of patriots and tyrants."

McVeigh was arrested within a few hours after the attack. Oklahoma State Trooper Charlie Hanger stopped McVeigh for driving without a license plate and subsequently arrested him for unlawfully carrying a weapon. McVeigh was convicted of the terrorist attack in Oklahoma City and sentenced to death.

McVeigh was proud of his "accomplishments." He believed that the Oklahoma City bombings had a positive effect on U.S. government policy, and he felt the peaceful resolution of the Montana Freeman standoff in 1996 was indicative of a new government policy. He was also proud of the $3.1 million settlement paid to survivors of Ruby Ridge.

McVeigh was motivated by a hatred for the government and hoped others would follow in his path. Watch for people carrying pamphlets and books espousing similar beliefs who may be planning to do so.

School Shooters

Ten years ago in 1999, Eric Harris and Dylan Klebold chose April 20 for their shooting spree at Columbine High School. They killed 12 students and a teacher and wounded 23 others. It was the deadliest massacre ever perpetrated in an American high school.

Harris and Klebold committed suicide prior to being apprehended by police, leaving no statements of motive for their actions. But there are several theories as to why they chose to act on April 20.

They made references to Waco and Oklahoma City, stating that they wanted their attack to be more spectacular. There is some evidence that their original attack was planned for April 19. Either way, they have etched April 20 as a date of concern for police. School shootings are a growing phenomenon, and it's possible that copycats could target their own schools on the anniversary of the Columbine shooting.

Heil Hitler

You may also see a spate of bias attacks, specifically anti-Semitic attacks, around April 20 because it is Adolph Hitler's birthday. Members of white supremacy groups see Hitler's birthday as a date of celebration. Most of these celebrations take place in private and do not attract the attention of law enforcement, but as April 20 approaches, you may want to review the symbols used by white supremacy groups to announce their presence.

The most obvious and well known of these symbols is the swastika. This twisted cross was the symbol of the Third Reich in Nazi Germany and remains a powerful symbol of hate. The presence of a swastika at a crime scene usually indicates a biased crime.

Other symbols that white supremacists and Nazis use to show praise to Adolph Hitler include the number "88." Translating the number "8" to the eighth letter of the alphabet "H" leads to "HH" or "Heil Hitler." Similarly, the number "18," for "A" and "H" may symbolize Adolph Hitler in certain contexts.

Smoking Out

Not only do neo-Nazis celebrate April 20, so do stoners. So you may encounter large groups of citizens rallying for the legalization of marijuana. April 20 (or 4/20) is recognized as National Pot Smoking day. This is obviously an informal movement, but as it gains momentum and popularity, large crowds may assemble.

The origins of 4:20 as code for "smoking out" are hazy but many attribute it to a group of California high school students who would assemble every day at 4:20 p.m. and smoke marijuana.

Over time, the term 4:20 has become closely associated with the drug culture, specifically marijuana. "4:20" is an indication that it is time to smoke marijuana. Many personal ads or advertisements for roommates will specifically say "4:20 friendly." The term has evolved to the point where on April 20 large groups assemble to smoke marijuana publicly. Though these groups traditionally have been peaceful, any time there is a large group under the influence of an intoxicant, you should be alert.

During a brief 48-hour period in April, police have seen crimes ranging from peaceful marijuana smoking to full-scaled terrorist attacks. Many of these events are difficult to prepare for, but knowing the anniversaries and significance of these events may help you proactively formulate a response.

Det. Joseph Petrocelli is a veteran of New Jersey law enforcement. You can comment on this article or reach the author by e-mailing the editor at David.Griffith@PoliceMag.com.