Hair-raising reports of grisly murders, often carried out in plain sight, offer chilling reminders to rival drug cartels and intervening authorities in Mexico's drug war. As the government scrambles to assert its control, who is responsible for the bloodshed?

Leaders with colorful nicknames and eccentric habits are trotted out before the media alongside seized drugs and weapons. The presentations are intended to show off the government's successes in stymying violence, yet the death toll continues to climb.

The various gangs terrorizing Mexico control different swathes of territory, trafficking illegal drugs up to the United States via several routes. The government's failed response to the trafficking, most notably President Felipe Calderon's crackdown beginning in December 2006, has resulted in the deaths of about 50,000 people. The recent election of Enrique Pena Nieto from Mexico's old ruling party, the PRI, suggests little will change.

Much of the violence is attributable to violent clashes between the two main cartels, Los Zetas and the Sinaloa cartel, and their allies. The Los Angeles Times explains:

In Mexico's eight most violent states, the battle has essentially boiled down to a no-holds-barred fight between two cartels: the Sinaloa network, Mexico's oldest and traditionally most powerful gang, and the newer and exceedingly vicious Zetas.

Mexico's network of drug cartels is vast and complex, with recent power struggles driving wedges between former allies and disbanding other groups entirely. Below, check out a few of the most notorious groups operating in the country:

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  • Los Zetas

    The Zetas are thought to have become the <a href="http://www.aljazeera.com/news/americas/2012/01/201212645739134301.html" target="_hplink">largest cartel</a> in Mexico recently, <a href="http://www.bbc.co.uk/news/world-latin-america-16712239" target="_hplink">operating</a> in over half the country's states. <b>Leader:</b> The notoriously brutal gangster <a href="http://www.huffingtonpost.com/2012/08/23/miguel-angel-trevino-zetas_n_1826236.html" target="_hplink">Miguel Angel Trevino Morales</a> (alias "Z-40") is believed to be the new leader of the Zetas drug cartel following a showdown with Heriberto "El Lazca" Lazcano. Trevino is infamous for human "cookouts" in which he stuffs people in oil drums and lights them on fire. "If you get called to a meeting with him, you're not going to come out of that meeting," a U.S. official <a href="http://www.huffingtonpost.com/2012/08/23/miguel-angel-trevino-zetas_n_1826236.html" target="_hplink">said of Trevino</a>. <strong>Territory:</strong> The Zetas control a swath of territory on Mexico's east coast extending along the Gulf of Mexico. <strong>Rivals:</strong> The Zetas are bitter rivals with the Sinaloa Cartel. In turn, the group is allied with the Beltran Leyva Cartel and the Tijuana Cartel. <strong>Notable incidents:</strong> In August 2011, gunmen <a href="http://www.huffingtonpost.com/2011/08/25/casino-royale-attack-leav_n_937413.html" target="_hplink">stormed the Casino Royale</a> in Monterrey and lit it on fire, killing dozens. In February 2012, 30 prisoners linked to the Zetas <a href="http://www.bbc.co.uk/news/world-latin-america-17135362" target="_hplink">broke free</a> from Apodaca jail during a riot. 44 inmates from the rival Gulf Cartel were killed. In May 2012, the Zetas cartel allegedly was involved in <a href="http://edition.cnn.com/2012/05/13/world/americas/mexico-remains/index.html" target="_hplink">dumping 49 decapitated bodies</a> on a busy highway near Monterrey. <em>Photo: Army soldiers flank Daniel Ramirez, alias "El Loco," during his presentation to the media in Mexico City, Monday, May 21, 2012. (AP Photo/Alexandre Meneghini)</em>

  • Sinaloa Cartel

    Mexico's second major cartel reportedly <a href="http://www.nytimes.com/2012/06/17/magazine/how-a-mexican-drug-cartel-makes-its-billions.html?pagewanted=all" target="_hplink">operates</a> in over a dozen countries, including trafficking cocaine and other drugs to the United States. <strong>Leader:</strong> Mexico's <a href="http://www.huffingtonpost.com/2012/08/07/joaquin-el-chapo-guzman-mexicos-most-wanted_n_1751671.html" target="_hplink">most-wanted drug lord</a>, Joaquin "El Chapo" Guzman, remains at large after he <a href="http://www.huffingtonpost.com/2012/08/07/joaquin-el-chapo-guzman-mexicos-most-wanted_n_1751671.html" target="_hplink">escaped from prison</a> by hiding in a laundry truck in 2001. In 2012, Guzman <a href="http://www.forbes.com/sites/erincarlyle/2012/03/13/billionaire-druglords-el-chapo-guzman-pablo-escobar-the-ochoa-brothers/" target="_hplink">appeared</a> on <em>Forbes</em>' list of billionaires for the fourth year in a row. <strong>Territory:</strong> The Sinaloa Cartel operates in northwestern Mexico (<a href="http://www.insightcrime.org/criminal-groups/mexico/sinaloa-cartel/item/192-sinaloa-cartel" target="_hplink">map</a>). <strong>Rivals:</strong> Arch-nemesis of Los Zetas, the Sinaloa cartel is <a href="http://www.insightcrime.org/criminal-groups/mexico/sinaloa-cartel/item/192-sinaloa-cartel" target="_hplink">allied</a> with the Gulf cartel and the Familia Michoacana. <strong>Notable Incidents:</strong> A 755-foot <a href="http://articles.latimes.com/2012/jul/12/nation/la-na-nn-drug-tunnel-details-20120712" target="_hplink">smuggling tunnel</a> running under a U.S. border fence was suspected to be operated by the Sinaloa cartel. The Sinaloa cartel may have been responsible for massacres in the border city of <a href="http://www.guardian.co.uk/world/2012/may/05/bodies-bridge-23-mexico-drug" target="_hplink">Nuevo Laredo in May 2012</a>. The bodies of 23 people <a href="http://www.guardian.co.uk/world/2012/may/05/bodies-bridge-23-mexico-drug" target="_hplink">were found</a> decapitated or hanging from a bridge, followed hours later by the discovery of 14 human heads in coolers near city hall. <em>Photo: In this June 10, 1993, file photo, Joaquin Guzman Loera, alias "El Chapo" Guzman, is shown to the press after his arrest at the high security prison of Almoloya de Juarez on the outskirts of Mexico City. (AP Photo/Damian Dovarganes, File)</em>

  • Gulf Cartel

    One of the oldest cartels, the Gulf Cartel recently has lost influence, but is <a href="http://www.insightcrime.org/criminal-groups/mexico/gulf-cartel" target="_hplink">backed up</a> by the Sinaloa cartel. <strong>Leader:</strong> Jorge Eduardo Costilla Sanchez, alias "El Coss." The U.S. has a <a href="http://www.state.gov/j/inl/narc/rewards/115354.htm" target="_hplink">$5 million bounty</a> on his head. Costilla Sanchez once allegedly held FBI and DEA agents at gunpoint with AK-47s and <a href="http://www.state.gov/j/inl/narc/rewards/115354.htm" target="_hplink">threatened</a> to kill them. <strong>Territory:</strong> The cartel operates out of the state of Tamaulipas, with other bases in Matamoros, Nuevo Laredo, and Reynosa, <a href="http://www.insightcrime.org/criminal-groups/mexico/gulf-cartel/item/90-gulf-cartel" target="_hplink">according to InsightCrime</a>. <strong>Rivals:</strong> The Gulf Cartel is allied with Sinaloa and enemies of Los Zetas. <strong>Notable Incident:</strong> In June, footage purporting to show masked members of the Gulf Cartel beheading Zetas members <a href="http://articles.nydailynews.com/2012-06-29/news/32475737_1_gulf-cartel-drug-cartel-leader-zetas-cartel" target="_hplink">surfaced online</a>. <em>Photo: From left: Andrea Escamilla Juarez ("La Negra," 21), Rene Cortez Zapata ("El Nicanor," 45), Nestor Hugo Del Angel Ferretis ("El Tango," 29), Jose De Jesus Mosqueda Mora ("El Chucho," 41), Jorge Fernando Larios Nossiff ("El Camaron", 57), and Ricardo Abraham Velazquez Del Castillo ("El Ricardillo, 24), all alleged members of a cell belonging to the Gulf Cartel criminal organization, are shown to the press by federal police in Mexico City, Friday, Dec. 9, 2011. (AP Photo/German Garcia)</em>

  • Juarez Cartel

    The Juarez Cartel reportedly <a href="http://www.insightcrime.org/criminal-groups/mexico/juarez-cartel" target="_hplink">smuggles</a> tons of narcotics into the U.S., using local gangs to <a href="http://www.insightcrime.org/criminal-groups/mexico/juarez-cartel" target="_hplink">act as enforcers</a>. <strong>Leader:</strong> Vicente Carrillo Fuentes, aka "<a href="http://www.time.com/time/specials/packages/article/0,28804,2019221_2019202_2019187,00.html" target="_hplink">The Viceroy</a>," has a $5 million bounty on his head from the U.S. government. <strong>Territory:</strong> Based in Ciudad Juarez, across the border from El Paso, Texas. <strong>Notable incidents:</strong> In July 2011, Antonio Acosta Hernandez ("El Diego") told police he had <a href="http://articles.cnn.com/2011-07-31/world/mexico.drug.arrest_1_lesley-enriquez-consulate-employee-drug-gang?_s=PM:WORLD" target="_hplink">ordered the killings</a> of 1,500 people. In 2010, a report suggested that an associate group of the Juarez Cartel was <a href="http://www.borderlandbeat.com/2010/08/juarez-cartel-trains-beautiful-women-as.html" target="_hplink">training beautiful</a>, young women as assassins. <strong>Rivals:</strong> Sinaloa cartel. <em>Photo: Jose Antonio Acosta Hernandez, 33, is presented to the media by federal police officers in Mexico City, Sunday July 31, 2011. According to federal officials, Acosta, nicknamed "El Diego," is a key drug cartel figure, who acknowledged ordering 1,500 killings. Authorities identified Acosta as head of La Linea, a gang of hit men and corrupt police officers who act as enforcers for the Juarez Cartel. (AP Photo/Marco Ugarte)</em>

  • Tijuana Cartel

    The Tijuana Cartel, aka the Arellano Felix Organization, <a href="http://www.insightcrime.org/criminal-groups/mexico/tijuana-cartel/item/193-tijuana-cartel" target="_hplink">operates</a> in the strategically important town of Tijuana, bordering San Diego, California. The cartel was depicted in the film '<a href="http://www.imdb.com/title/tt0181865/" target="_hplink">Traffic</a>' (2000). The cartel has been <a href="http://www.insightcrime.org/criminal-groups/mexico/tijuana-cartel" target="_hplink">weakened</a> by infighting. <strong>Leader:</strong> Fernando Sanchez Arellano, alias "El Ingeniero." (The "Engineer.") <strong>Territory:</strong> Baja California <strong>Notable Incident:</strong> The cartel allegedly dissolved bodies using chemicals or burned them in the desert to <a href="http://www.cbsnews.com/8301-202_162-57408368/tijuana-cartel-leader-arellano-felix-gets-25-yrs/" target="_hplink">cover their tracks</a>. <em>Photo: Seized drugs and packages of marijuana and crystal meth are displayed during a presentation to the press in Tijuana, Mexico, Wednesday, March 24, 2010. (AP Photo/Guillermo Arias)</em>

  • Knights Templar

    The Knights Templar are a bizarre, cult-like group. <a href="http://www.guardian.co.uk/world/2012/aug/26/mexican-corpses-acapulco" target="_hplink">The Guardian writes</a>: "Propaganda from the Knights Templar blends a mix of Michoacan regionalism, Christianity and revolutionary slogans." The Knights Templar are a major trafficker of methamphetamine. <strong>Leader:</strong> Servando Gómez Martínez, alias "La Tuta," <a href="http://www.insightcrime.org/insight-latest-news/item/3085-knights-templar-leader-appears-in-video" target="_hplink">denied</a> in a filmed address that the Knights Templar are a cartel. Gómez Martínez is also called "El Profe" ("The Professor"), and <a href="http://www.insightcrime.org/component/k2/item/319-familia-michoacana-leader-reportedly-employed-as-teacher" target="_hplink">InSight reports</a> that Gómez Martínez was still a publicly-employed teacher as of 2010. <strong>Notable Incident:</strong> The group recently was <a href="http://www.huffingtonpost.com/2012/05/28/sabritas-firebombing-attack_n_1551355.html" target="_hplink">blamed</a> for coordinated firebombings of a PepsiCo subsiadary. It was a Mexican drug cartel's first attack on a transnational company. <strong>Rivals:</strong> Los Zetas. <em>Photo: Juan Gabriel Orozco Favela, alias "El Gasca," an alleged member of the Knights Templar drug cartel, is escorted by Mexican Army soldiers as he is presented to the media in Mexico City, Tuesday, Nov. 15, 2011. (AP Photo/Alexandre Meneghini)</em>

  • Beltran Leyva (Disbanded)

    The Beltran Leyva largely disbanded following a power struggle after the death of its leader, Arturo Beltrán Leyva. <strong>Leader:</strong> Héctor Beltrán Leyva, alias "El Ingeniero," or "El H," is wanted for up to <a href="http://www.state.gov/j/inl/narc/rewards/133311.htm" target="_hplink">$5 million</a> in the U.S. He is the brother of former cartel leader Arturo Beltrán Leyva. <strong>Territory:</strong> Northern Sinaloa. <strong>Rivals:</strong> Allied with Los Zetas after <a href="http://www.cbc.ca/news/world/story/2011/08/28/f-mexico-drug-cartels.html" target="_hplink">splitting from Sinaloa</a> in 2008. <strong>Notable incident:</strong> Former cartel chief Arturo Beltrán Leyva died in a <a href="http://latimesblogs.latimes.com/laplaza/2009/12/mexico-drug-lord-arturo-beltran-leyva-mexican-navy-marines-raid-felipe-calderon-drug-war.html" target="_hplink">shootout</a> involving 200 Mexican marines in late 2009. <em>Photo: In this photo released by Mexico's Navy, Navy marines arrest alleged drug kingpin Sergio Villarreal Barragan, alias "El Grande," center, in Puebla, Mexico, Sunday Sept. 12, 2010. (AP Photo/Mexican Navy)</em>

  • La Familia Michoacana (Extinct)

    La Familia Michoacana, a pseudo-religious gang, has been largely <a href="http://www.excelsior.com.mx/index.php?m=nota&id_nota=779205&rss=1" target="_hplink">disbanded</a>. <strong>Leader: </strong> Nazario Moreno González, alias "El Más Loco" ("The Craziest One"), died in December 2010. <em>Photo: Martin Rosales Magana, aka "El Terry" and alleged leader of the Mexican La Familia drug cartel, is escorted by police officers during his presentation to the media in Mexico City, Wednesday, Oct. 5, 2011. Authorities allege Rosales is one of the last major leaders of the La Familia cartel. (AP Photo/Leonardo Casas)</em>

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