" The bombing of the Alfred P . Murrah Federal Building in Oklahoma City , bombing Conflict.Attack.DetonateExplode , on April 19 , 1995 , was , at the time , the most significant act of terrorism that had ever taken place in the United States . act Conflict.Attack.Unspecified agencies , led by the Federal Bureau of Investigation ( FBI ) , immediately began an extensive investigation to identify and prosecute the culprits . The investigation , known as investigation Cognitive.Research.Unspecified , was run by a Task Force that investigation Cognitive.Research.Unspecified primarily of FBI investigators and support personnel and Department of Justice prosecutors . Within a few months , three individuals - Timothy McVeigh , Terry Nichols , and Michael Fortier - were indicted for crimes relating to the bombing . McVeigh and Nichols were convicted indicted Justice.ChargeIndict.Unspecified trials , and Fortier pled guilty as part of a plea convicted Justice.Convict.Unspecified with the government . McVeigh , guilty Justice.Convict.Unspecified had devised the plot to bomb the Murrah Building and had planted the bomb , was sentenced to bomb Conflict.Attack.DetonateExplode . On May 8 , 2001 , one week before sentenced Justice.Sentence.Unspecified ' s scheduled execution date , the Department of Justice and the FBI revealed to McVeigh ' s and Nichols ' attorneys that over 700 investigative revealed Justice.InvestigateCrime.Unspecified had not been disclosed to the defendants before their trials . The government acknowledged that it had violated a discovery order in the case , and the Attorney General stayed McVeigh ' discovery Justice.InvestigateCrime.Unspecified execution for one month in order to resolve the legal issues arising from the belated disclosure . Following the public revelation of the problem , and after finding and releasing more than 300 additional OKBOMB documents to the defense , finding Justice.InvestigateCrime.Unspecified FBI came under severe criticism for its handling of the OKBOMB documents . "

Here is a look at some of the critical pieces of evidence presented during the trial . Taken as a whole , the evidence suggests that the plan to bomb Conflict.Attack.DetonateExplode the Boston Marathon took shape over three months .