The stated objective of the rally was to bring attention to the plight of the large population of illegal immigrants in Los Angeles and the US as a whole. Organizers obtained all the necessary permits to hold a rally at MacArthur Park on May 1, 2007 until 21:00. At about 17:15 a few protesters began blocking the street, which the rally permit expressly prohibited. Police commanders declared the gathering an unlawful assembly and gave the command for the crowd to disperse. The order was broadcast from a police helicopter circling the park, from police cars, and from hand-held megaphones, before police officers in riot gear formed a line and advanced slowly to clear the area. The officers proceeded about 50 feet at a time, allowing those complying with the dispersal order to retreat. The orders were given in English to a crowd of mostly Spanish speaking demonstrators.
Altogether, the estimated 600 police officers fired 146 foam-rubber projectiles. 27 marchers and 9 members of the media were injured, 5 people were arrested, and at least 50 civilians filed complaints with the LAPD regarding mistreatment by officers. 7 to 15 police officers were injured.
The incident has received considerable attention from news media because several reporters were also pushed and injured, notably Christina Gonzalez from L.A.'s Fox 11 News (KTTV), and Telemundo's National Evening Broadcaster, Pedro Sevcec. Sanjukta Paul, a National Lawyer's Guild observer, was beaten repeatedly by a LAPD officer, including a blow to the kidneys, as she attempted to separate police from the crowd. CBS 2/KCAL 9 (KCBS-TV, KCAL-TV) reporter Mark Coogan and his cameraman Carl Stein were also accosted. Stein was struck on the ribs by LAPD batons.  Patricia Nazario, a reporter for KPCC, was beaten in the ribs and back, before being struck over the head with a baton. ABC 7 (KABC-TV) reporter Sid Garcia was hit by a rubber bullet, but it ricocheted off him. Patti Ballaz, a camerawoman for KTTV who was injured, filed a claim for unspecified damages against the city and the police department.
Response by government officials
At a press conference later in the day, Police Chief William J. Bratton indicated that an investigation was underway to "determine if the use of force was appropriate," going on to state that "the vast majority of people who were [at MacArthur Park] were behaving appropriately."  Bratton indicated he may ask the FBI to investigate the chain of events.
At the time of the events, Los Angeles Mayor Antonio Villaraigosa was on a trip to El Salvador. He cut his trip short three days later, in order to personally oversee the investigation of the chain of events, and asked Police Chief Bratton to oversee a "complete and comprehensive review of this incident, including deployment, tactics, and use of force."  At a Sunday morning mass at Cathedral of Our Lady of the Angels on May 6, Villaraigosa said "I come today with a heavy heart ... Nobody, nobody should be victimized in a way we saw women, children and families victimized just a few days ago."
Los Angeles city council member Herb Wesson, whose district includes neighborhoods near MacArthur Park, criticized the police response by comparing it to beating of civil rights leaders in the South in the 1960s. He praised Bratton's response, though, saying "I'm proud that the chief said quickly that some inappropriate actions took place."  Fabian Núñez, Speaker of the California Assembly whose district includes MacArthur Park where the events took place, condemned the actions of the police by saying "To say we are outraged is an understatement ... We want those responsible in the highest levels of the LAPD to pay consequences." Robert Baker, president of the Police union, responded, calling Wesson's and Núñez's words "police bashing that erroneously insinuates racial bias". 
Four separate investigations were created to investigate the incident, one of them being a special task force set up by city council president Eric Garcetti. The task force is composed of five councilmembers, and is co-chaired by Los Angeles city councilmembers Ed Reyes and Jack Weiss.  The FBI also investigated the incidents for civil rights violations. 
On May 17, the American Civil Liberties Union filed a request with U.S. District Judge Gary A. Feess to look into whether the incident at MacArthur Park violated a 2001 consent decree which was a result of the Rampart scandal. If the judge finds the LAPD in violation of the decree, federal oversight of the LAPD could be extended beyond the current deadline of 2009. 
On May 29, Chief Bratton presented preliminary findings of an internal police investigation to the civilian police commission, and on May 30 he presented the preliminary findings to the Los Angeles City Council. According to Bratton, the main reasons for the mêlée were "a command and control breakdown," [which] began at the planning stages and dominoed throughout the event itself". 
On October 9, 5 months after the incident, the LAPD released the results of an internal investigation.
On May 17, approximately 2,000 to 3,000 people marched in protest of the events that took place on May 1. The march started at a church 10 blocks west of MacArthur Park with a "town hall meeting", and ended at MacArthur Park. The march was peaceful, without a single arrest, and the town hall meeting featured speakers such as Mayor Antonio Villaraigosa and Assembly Speaker Fabian Núñez, who later marched with the protesters. Police Chief William Bratton was also present at the march and town hall meeting.
On May 7, 2007 Chief William J. Bratton announced a departmental reorganization. Cayler "Lee" Carter, who was a deputy chief and the highest ranking official at scene, was demoted to commander and assigned home duty. On May 17, Carter announced his resignation from the LAPD, effective June 6. In his May 7 announcement, Bratton also announced that Carter's deputy, Louis Gray, would be reassigned to the operations bureau, and that about 60 officers who were involved in the incident would be taken off the street, pending the outcome of the investigations.
On May 9, the Multi-Ethnic Immigrant Workers Organizing Network filed a class-action suit against the Los Angeles Police Department and the city. In November 2008, it was disclosed that the city was in negotiations and was willing to pay as much as $13 million to settle the lawsuits.
On May 30, Bratton announced the creation of a new Incident Management & Training Bureau, and assigned Deputy Chief Michael Hillmann to head the newly created bureau.
Over a year later, on July 8, 2008, the LAPD announced "that 17 officers and two sergeants from the department's elite Metropolitan Division should be punished for their roles in [the incident]". The recommended punishment was not publicized, and could range from a simple reprimand to termination. Critics criticized the announcement, saying that only officers "whose actions were captured on video" were recommended for punishment.
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16.^ Bob Pool (May 7, 2007). "Villaraigosa visits site of May Day melee". Los Angeles Times.
17.^ Patrick McGreevy (May 2, 2007). "Bratton oversees LAPD inquiry at critical time". Los Angeles Times.
18.^ "Saturday In The Park Is Quiet As Protesters Are No-Shows". May 5, 2007.
19.^ "MacArthur Park Peaceful Immigration Rally". Associated Press. May 19, 2007.
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