The printing plant of the Los Angeles Times on the corner of 1st Street and Broadway was rocked by an explosion at 1:07 AM on October 1, 1910 and ignited several tons of flammable ink stored there. Amazingly only 17 people were hurt, and 20 killed despite more than 100 workers were in the plant at the time of the explosion who were preparing the morning paper.
The bombing of the Times' plant was early on pointed at unionists due to the newspaper's strong oppostion of labor unions. The Times had encouraged the city to impose anti-picketing ordinances, allowing police to arrest any protestors or people speaking "unusually loud" following the large number of strikes that erupted in Los Angeles the previous summer. Predicatably, this resulted in angry labor leaders who believed that they were making headways in the city, and Secretary-Treasurer John McNamara of the International Association of Bridge and Structural Iron Workers Union sent in his brother James and associate Ortie McManigal to resolve the issue.
Following the attack, the city began a massive investigation into the incident and eventually focused on the McNamara brothers who were extradited to Los Angeles and plead "not guilty" at their preliminary. Union supporters around the nation where quick to rally and persuaded Clarence Darrow to take the case.
The defense's case was bad from the start, the prosecution had a rock-solid case against the brothers. On top of that, an associate of Darrow was charged with attempting to bribe jurors and Darrow himself was charged with jury tampering. However, in the case of Darrow's 2 counts of bribery, 1 count was aquitted, and the other failed to reach a verdict.
Early on in the trial, Darrow himself became convinced that the brothers were guilty and faced death row if they went to trial. Eventually prosecutors (fearing the brothers would become union marytrs) and Darrow (for above reasons) were persuaded to negotiate. The brothers plead guilty. James was sentence to life in prison for the actual bombing. John was sentenced to 15 years for conspiring to bomb the printing plant. The bombing effectively ended any attempts in the early part of the 20th century to make Los Angeles a union city.
Sources
http://www.losangelesalmanac.com/topics/History/hi06e.htm
http://www.latimes.com/services/site/la-facts-milestones.story