Federal prosecutors have linked two men accused in the execution-style murder of a drug cartel lawyer in Southlake nearly three years ago to as many as 12 other slayings, according to court documents obtained by NBC 5.

Juan Jesus Guerrero Chapa, the personal lawyer for the one-time leader of the powerful Gulf Cartel, was gunned down in May 2013 as he and his wife were getting in their Range Rover after shopping at Southlake Town Square.

His wife wasn't injured.

In recently-filed court papers, prosecutors claim two of the three men arrested for stalking Guerrero were involved in a years-long killing spree in Mexico's third-largest city, Monterrey, only a two-hour drive south of the Texas-Mexico border.

In the most recent slaying, the Southlake victim's brother-in-law was murdered in Monterrey in February.

Prosecutors claim emails obtained by federal agents link Jesus Gerardo Ledezma-Cepeda, 59, and his son, Jesus Gerardo Ledezma-Campano Jr., 32, to the string of murders. The Ledezmas were one-time police officers in Mexico.

A third defendant, Jose Luis Cepeda-Cortes, 59, faces the same charges in the Southlake murder but is accused of being involved in only one of the other slayings. Cepeda-Cortes is Ledezma-Cepeda's cousin.

The three, all Mexican citizens, are not accused of being the actual shooters in the Southlake attack. Instead, they are portrayed by prosecutors as running a sophisticated intelligence wing for a cartel hit squad. The cartel is not identified.

The three placed an electronic tracking device on Guerrero's vehicle and even used remote cameras placed in his upscale Southlake neighborhood to track his movements leading up to the murder, according to their indictment.

Their trial, set for next month in federal court in Fort Worth, promises to lay bare the inner workings of cartels and the government agents targeting them.

Guerrero, who was living quietly with his wife and children in a $1.3 million Southlake mansion, was a U.S. government informant, NBC 5 has reported.

In a separate court filing which hints at the men's defense, attorneys for one of the accused wrote that they will ask government witnesses about Guerrero's "illegal activities" while he was an informant living in Southlake.

LINKS TO 12 MURDERS

According to U.S. prosecutors, the men were involved in the following murders both before and after the Southlake attack:

Luis Cortes Ochoa , the former undersecretary of security in the Monterrey suburb of San Pedro Garza. He was gunned down in his pickup on Feb. 24, 2010. Ledezma-Campano and Ledezma-Cepeda had placed a tracking device on his vehicle, prosecutors said.

, the former undersecretary of security in the Monterrey suburb of San Pedro Garza. He was gunned down in his pickup on Feb. 24, 2010. Ledezma-Campano and Ledezma-Cepeda had placed a tracking device on his vehicle, prosecutors said. Dionicio Cantu Rendon, he was reported missing on Feb. 3, 2012, and is presumed dead. Ledezma-Cepeda's emails link him to the slaying, prosecutors said. Cantu is not identified further and no other details were mentioned in the court document.

he was reported missing on Feb. 3, 2012, and is presumed dead. Ledezma-Cepeda's emails link him to the slaying, prosecutors said. Cantu is not identified further and no other details were mentioned in the court document. Eliseo Martinez Elizondo , who was murdered almost exactly a month before Guerrero. All three suspects followed him using the same tracking device they used to follow Guerrero, prosecutors said. Elizondo also was a U.S. informant and, like Guerrero, was involved with Mexican casinos, according to the Monterrey newspaper Reporte Indigo.

, who was murdered almost exactly a month before Guerrero. All three suspects followed him using the same tracking device they used to follow Guerrero, prosecutors said. Elizondo also was a U.S. informant and, like Guerrero, was involved with Mexican casinos, according to the Monterrey newspaper Reporte Indigo. Felipe Cantu Lozano , found murdered on Sept. 30, 2013.

, found murdered on Sept. 30, 2013. Juan Cantu Cuellar , killed the same day. Investigators found the victims' names in Ledezma-Cepeda's emails. The content of the emails was not disclosed and no other details of the murders were released.

, killed the same day. Investigators found the victims' names in Ledezma-Cepeda's emails. The content of the emails was not disclosed and no other details of the murders were released. Hector Javier Alvarez Reyna , 47, was gunned down in Monterrey the following month. He was killed near his mother's business where he worked. According to Mexican news reports, Alvarez was an ex-con who had served time for drug-related crimes. Prosecutors reported finding Alvarez's name in Ledezma-Cepeda's emails.

, 47, was gunned down in Monterrey the following month. He was killed near his mother's business where he worked. According to Mexican news reports, Alvarez was an ex-con who had served time for drug-related crimes. Prosecutors reported finding Alvarez's name in Ledezma-Cepeda's emails. Rolando Caballero Diaz . The Ledezmas tracked him in August 2014 and he was "subsequently kidnapped and presumed dead," prosecutors say.

. The Ledezmas tracked him in August 2014 and he was "subsequently kidnapped and presumed dead," prosecutors say. Artemio Gonzales-Wong , a top police official in the Monterrey suburb of Guadalupe, and three others. The four were gunned down in a vehicle while driving down a Monterrey street on Oct. 27, 2014. The leader of a political organization, Humberto Reyes Martinez, was gravely wounded in the attack and died nine months later.

, a top police official in the Monterrey suburb of Guadalupe, and three others. The four were gunned down in a vehicle while driving down a Monterrey street on Oct. 27, 2014. The leader of a political organization, Humberto Reyes Martinez, was gravely wounded in the attack and died nine months later. Moises Tijerina de la Garza, Guerrero's brother-in-law and former municipal treasurer in a Monterrey suburb. On Feb. 23, 2016, he was shot six times with a 9-millimeter pistol when he walked out of a Monterrey bakery, according to Mexican news reports. His name also was found in the men's previous emails, prosecutors said.

At the time of their arrests in September 2014, Ledezma-Cepeda and Ledezma-Campano were still searching for two other men, including Guerrero's brother, Armando Guerrero-Chapa, according to the court document.

GUERRERO'S BACKGROUND

Guerrero was the personal lawyer for Osiel Cardenas Guillen, the longtime head of Mexico's Gulf Cartel who has been described as one of the most brutal drug kingpins in Mexican history.

Cardenas was arrested in Mexico in March 2003 but it was widely reported that he continued directing his drug empire from behind bars. He was later extradited to the U.S.

In an extraordinary deal in 2010, Cardenas agreed to cooperate with U.S. investigators and was sentenced to just 25 years in prison.

With Cardenas behind bars, the Zetas, which had been enforcers for the Gulf Cartel, broke off to become their own group. The Zetas and the Gulf cartels then engaged in a bloody battle for control of certain drug routes, according to drug experts.

A "narcomanta," a public message on cloth posted by the Zetas in 2012, threatened Cardenas and Guerrero.

DEFENDANTS HELPED DRUG DEALER FLEE: PROSECUTORS

According to prosecutors, the father and son Ledezmas continued participating in other cartel activities in the U.S. in the months after Guerrero's murder, helping an accused drug dealer named Casimiro Bautista flee. An indictment in October 2013 accused Bautista of running a large-scale marijuana smuggling operation.

The Ledezmas picked him up near the U.S.-Mexico border "at the time of his flight," prosecutors say.

Bautista was rearrested and in January agreed to a plea agreement, admitting he had transported more than 1,000 kilograms of marijuana from Mexico, through the Rio Grande Valley, and to regional distributors in Tennessee and Florida in hidden compartments in semi-trucks and campers.

Bautista, also known as "Vecino" or "Sasquatch," agreed to forfeit $1.5 million. He has not yet been sentenced.

DEFENSE TO ASK ABOUT VICTIM'S "ILLEGAL ACTIVITIES" WHILE U.S. INFORMANT

Attorneys for one defendant, Cepeda-Cortes, filed a list of potential witnesses 57 names long. They include 19 FBI agents, 11 DEA agents and assorted other investigators and experts.

The defendant's attorney said the witnesses would testify about the information Guerrero provided to federal agents about Mexican drug cartels that led to the U.S. seizure of cartels' "assets."

The attorney said the information "ultimately resulted in the kidnapping and release of [Guerrero's] family based on the agreement that those organizations would no longer be targeted by [Guerrero]."

It did not specify when the kidnapping happened or whether it occurred in Southlake or somewhere else.

The attorneys also said their witnesses "will testify regarding the investigation into the illegal activities of [Guerrero] while [Guerrero]was a [U.S.] informant" and "the means used specifically by his drug operation to avoid interference from law enforcement."

A Blackberry employee is expected to testify about Blackberry's messaging system, which is known for its encryption, and "records related to the use of Blackberry phones."

An employee of Blackline GPS, a company which rents satellite tracking devices, will testify about the electronic gadgets allegedly used by the defendants and placed on Guerrero's car.

A person only identified as a "cooperating witness" will talk about the "language used among drug dealers."

Government prosecutors wanted 60 hours to present their case. U.S. District Judge Terry Means is giving them 35.

The trial is set to start at 10 a.m. on April 25.

Government Motion to Use Evidence

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