Ariel Máximo Cantero, alias “Guille,” is the leader of the Monos, a family clan and drug gang based in Rosario, Argentina. Cantero is currently in prison. However, that has not stopped him from calling the shots from behind bars.

Criminal History

Cantero, alias “Guille,” is the son of Los Monos founder, Ariel Cantero, alias “El Viejo,” and Patricia Celestina Contreras de Cantero, alias “La Cele.”

Guille assumed leadership of the Monos family clan in 2013, along with his foster care brother Ramón Manchuca, alias “Monchi,” following the murder of his brother, Claudio Ariel Cantero, alias “El Pájaro.”

In the wake of his brother’s murder, Cantero oversaw a wave of violence in Rosario that resulted in the local homicide rate shooting up far higher than the national average.

Among those murdered immediately after El Pájaro’s death was nightclub owner Diego Demarre, who Cantero and the Monos believed turned the former leader over to his assassins. Police suspected Cantero of the murder.

Wanted for murder and for leading the Monos, Cantero went to the police station and asked to speak with agents saying his name was “Diego Oviedo.” However, investigators recognized him, and he was taken into custody under his real identity. Guille hoped to be released soon as he had no convictions or significant judicial record at that time. However, that was about to change.

Over the next few years, Cantero was charged with drug trafficking (2015, 2018, 2019), illicit associations as the leader of the Monos (2018), homicide (2018), and kidnapping (2019).

Cantero is known to use violence to intimidate authorities. In 2018, just days after Cantero was sentenced to 37 years in prison on charges of illicit association and homicide, a gunman opened fire on the former house of one of the judges. This was the first of a series of attacks against judges and judicial buildings in Rosario.

In July 2020, investigators proved that Cantero threatened a judge for denying his request to be transferred to a different prison.

Cantero has continued to issue orders and threats from behind bars. On August 23, 2021, a landline phone intended for all prisoners was discovered in Cantero’s cell. The line was not monitored, and his conversations were not recorded – potentially allowing the criminal leader to continue his illegal activities behind bars. The landline was removed but, two weeks later, an inspection on September 2 found that it had been replaced. Likewise, in June 2018, 42 cellphones were found in the prison wing where Cantero and other Monos members were held, an area only accessible by prison personnel.

The threats continued in 2021, in the lead-up to the court decision regarding Cantero’s role in ordering the 2018 attacks. Santa Fe’s 911 line received an anonymous phone call in early September, saying “Release the Canteros, free the Monos or we will kill all the prosecutors.” Then, on August 18, the day before the trial began, two gunmen opened fire on the courthouse – the very sort of attack that the Monos leader has been charged with ordering in 2018.

The murder rate also spiked around this time. Rosario saw six homicides in a 24-hour period between September 6 and 7.

On September 30, 2021, Cantero was sentenced to 22 more years for ordering the 2018 attacks on the homes of judicial officials and buildings. Since then, however, Cantero’s control of the Monos does not appear to have waned. His family remains firmly in control of the gang, as evidenced by the arrest of his younger brother, Dylan, in September 2022.

Criminal Activities

In addition to the Monos’ regular drug sale activities, Cantero has turned violence into one of the group’s most profitable criminal activities. Through threats, extortion and usurpations, he has reportedly amassed more than 150 properties. For example, businessman Leonardo Peiti, handed his clandestine casinos over to Cantero upon receiving death threats.

Since 2013, Cantero has managed to continue issuing orders from behind bars – a capacity that Cantero has publicly flaunted despite being transferred to six different prisons. When asked to declare his profession during a recent court hearing, Cantero boldly responded: “I hire hitmen to shoot judges.”  

Prosecutors have proven that Cantero has used WhatsApp to coordinate attacks from behind bars, and in 2021 a landline phone was twice discovered in Cantero’s cell. Cantero is also known to have used “paid visitors” to communicate orders.


Cantero grew up in the La Granada neighborhood in the southern part of Rosario, in Argentina’s Santa Fe province. Los Monos have operated in the city of Rosario, Argentina’s third most populous city, for more than 20 years. Located on the west bank of the Paraná River, Rosario is a transit point for drug and contraband shipments coming from neighboring Bolivia and Paraguay.

Cantero is currently being held in the Marcos Paz Federal Penitentiary in Buenos Aires.

Allies and Enemies

Cantero counts corrupt public officials among his allies, as demonstrated by the ease with which he has managed to access phones within the prison.

Additionally, with the help of his right-hand man, Brandon Baya, Cantero has also formed alliances with other gangs in neighboring cities, such as San Lorenzo, Capitán Bermúdez and Granadero Baigorria.

Cantero has also accrued many enemies. Cantero’s archenemy is rival Rosario-based drug trafficker Esteban Alvarado, who is also behind bars at the Marcos Paz Federal Penitentiary. Both Cantero and Alvarado are known to try to incriminate the other in different crimes with the help of complicit police. A division of the judicial police even reportedly aimed to take out Cantero to facilitate a territorial takeover by Alvarado’s group.  

Guille’s arrest, along with the arrests of other key members of the Monos, gave rise to a power struggle with other local gangs, such as the Funes and the Ungaro, over the control of street-level drug sales.


With seven sentences for different crimes – Cantero has already accumulated more than 83 years of prison time. While Guille’s prison sentence is likely to keep getting longer, that alone is not going to be enough to reign in his influence over Rosario’s criminal landscape. As long as Cantero can keep issuing orders from behind bars, he will continue to pose a major threat to security in Rosario.

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