Today marks the four-year anniversary of the tragic bombing that took place at the Boston Marathon on April 15, 2013. Three people were killed and at least 264 were injured in the double blasts.

Even though the September 11th attacks are reportedly the worst in U.S. history, the Boston Marathon bombing still resonates with the many citizens that were present during the attack and continues to send shock waves across the nation.

The Boston Marathon four years ago

The finish line-turned-burial-ground for runners at the marathon was laden with homemade bombs going off just seconds apart.

Several runners lost their limbs while others ultimately lost their lives.

Runners and attendees reported the day as a perfect day for a marathon—no one suspected the tragic event that would take place near the finish line.

The suspects were later identified as brothers, Tamerlan Tsarnaev, 26, and Dzhokhar Tsarnaev, 19. Reportedly, the brothers had several accomplices, some which were later charged with lying to federal officials.

Soon after the Boston Marathon bombing, the brothers carjacked a driver in Cambridge, Massachusetts. Subsequently, a police officer, Sean Collier was also shot and killed. As the brothers were being chased, they exchanged gunfire with local law enforcement and they reportedly threw explosives out of their car windows at the officers.

Both brothers illegally immigrated to the United States. One brother, Tamerlan, was identified by police as being killed during the aforementioned police encounter. Tsarnaev, 19, continued to run from authorities and was eventually apprehended on April 19, 2013.

Reportedly, Tsarnaev pleaded “not guilty” on at least 30 charges involved with the Boston Marathon bombing.

Tragic events in the U.S.; incidents of mass violence

The Alfred P. Murrah Federal Building in Oklahoma City, Oklahoma, is no stranger to mass violence on U.S. soil. On April 19, 1995, Timothy McVeigh and his accomplice, Terry Nichols coordinated a truck-bomb explosion that left 168 dead and hundreds more injured; among the death toll included 19 young children.

Until September 11, 2001, the Oklahoma City bombings were the most notorious for their mass violence and domestic-terrorist genre of fear on U.S. soil.

Reportedly, schools and places of business are the most likely places to be targeted in regards to incidents of mass violence, says CNN.

Today, social media platforms are trying to sympathize by tagging #Onebostonday in an effort to remember the Boston Marathon Bombing and to pay homage to those that lose their lives and had their lives affected.