Citing a gruesome series of killings in Los Angeles in which one victim was dismembered and whose heart was cut out, a federal grand jury has indicted 22 alleged members or associates of the notorious MS-13 gang on charges that include racketeering and murder.

Five of the seven killings outlined in a new indictment involved the victims’ bodies being dumped in Angeles National Forest, according to court documents.

U.S. Attorney Nick Hanna said the gang is "believed to have killed 24 people over the past two years" in Los Angeles.

"This investigation has been an unqualified success," Hanna said. "The collaborative law enforcement effort solved several murder cases and dealt a severe blow to members of the gang who engaged in acts of brutality not seen in the region for over 20 years."

The 78-page grand jury indictment says 22 alleged members and associates of the MS-13 Fulton clique, based in the Los Angeles suburbs of the San Fernando Valley, engaged in common street gang business: narcotics sales, robberies, burglaries and extortion schemes.

But the indictment also details how those charged also used horrific violence to control members, protect territory and intimidate rivals.

The case is the culmination of a two-year investigation by the FBI, Los Angeles Police Department and Los Angeles County Sheriff’s Department.

Formed in Los Angeles in the mid-1980s, MS-13, also known as Mara Salvatrucha, has a footprint in at least 10 states, including California, New York, Virginia, Maryland and Texas, as well as several Central American countries, including El Salvador, Honduras, Mexico and Guatemala.

Fulton is one of at least 20 subsets, or cliques, of the gang operating around Los Angeles, and federal prosecutors said it modeled itself after a subset of the gang in El Salvador known as “503.” That group broke away, the indictment alleges, and became more violent after the El Salvadoran government tried to quell violence by arranging a secret truce with older MS-13 leaders.

Salvadoran MS-13 members who were recent arrivals to Los Angeles often identified with the 503 group and joined with Fulton members to carry out the slayings detailed in the indictment, the court papers allege.

In Los Angeles beginning in 2017, MS-13 members who identified with the 503 group had been required to kill a gang rival or "someone perceived to be adverse to MS-13" in order to be initiated, the indictment says.

The indictment also suggests that the Fulton group operated differently from other MS-13 cliques in Los Angeles.

"MS-13 in Los Angeles was distinct from MS-13 cliques in other parts of the country, because in Los Angeles, MS-13 had to pay extortionate rent payments to the Mexican Mafia, to which MS-13 swore fealty," the indictment states.

Among the seven murders at the center of the 12-count indictment was the killing of an individual identified as "J.S.," who federal prosecutors said was choked and dismembered in March 2017 for crossing out MS-13 graffiti.

One alleged gang member "carved out J.S.'s heart," and others "threw J.S.'s body parts into a canyon" in the Angeles Forest, the indictment says.

A month later, another victim, identified as G.B., was struck on the back of the head with a pistol and hacked to death with a machete, according to the court filing. His body was found close to the first dump site in the forest.

Federal prosecutors said some of the MS-13 gang members suspected G.B. was an informant. The indictment says that MS-13 had "zero tolerance" for members or associates who cooperate with law enforcement and that once suspected, a "green light" could be issued authorizing that person be killed on sight.

In June 2017, a man identified in the indictment as E.H. was killed with a machete and a knife.

Authorities said non-gang members were also targeted, including a 34-year-old homeless man who was shot to death in January in a North Hollywood park claimed by the gang.

Court documents said some of those charged posted photographs and messages to Facebook and other social media that appeared linked to the violence. Images showed the alleged gang members posing with weapons and in gang attire, and some of the pictures were taken close to the murder scenes and body dump sites.

Multiple law enforcement sources told NBC News that investigators think the number of killings connected to the gang could be much higher than those detailed in the indictment.

The charges in the indictment include allegations of a racketeering conspiracy against some defendants, murder and violent crimes in aid of racketeering.

Named in the indictment are German Arnulfo Cruz Hernandez; Angel Amadeo Guzman; Ever Joel Morales; Fernando Garcia Parada; Jose Baquiax Alvarez; Kevin Villalta Gomez; Kevin Arteaga; Edgard Velasquez; Walter Chavez Larin; Yefri Alexander Revelo; Wilfredo Vides; Gerardo Alvarado; Roberto Carlos Mendez Cruz; Bryan Alberto Ordones; Roberto Alejandro Corado Ortiz; Edwin Isaac Mendez; Josue Balmore Flores Castro; Luis Arturo Gonzalez; Edwin Martinez; Steven Emmanuel Linares; Marco Antonio Ramos; and Erick Eduardo Rosales Arias.

All 22 who are charged are in custody, and four of the arrests were made by law enforcement over the last three days, Hanna, the U.S. attorney, said Tuesday.

Hanna said that many of the people indicted are "extremely young" — only three of the 22 named in the indictment are older than 24 — and many came into the country within the last four years.

Nineteen of the 22 defendants "are in the country illegally," he said, two are U.S. citizens and one is a lawful permanent resident. Many of the victims are also recent immigrants to the U.S., Hanna said.

"So, as you can see, they are preying on their own community — and that's what we're here to stop," he said. He said most of the 22 "directly participated in a killing spree over the past two years."

Sixteen charged in connection with six murders charged as violent crimes committed in aid of racketeering are eligible for the death penalty, but federal prosecutors have not made a determination as to whether to seek the penalty if those people are convicted, the U.S. attorney's office said.

Those six killings were committed "in an especially heinous, cruel, or depraved manner” that involved torture or serious physical abuse, the U.S. attorney’s office said.

MS-13 was formed in Los Angeles in the 1980s by refugees who fled civil conflict in El Salvador, and it is organized in a loose structure of cells or "cliques," that control specific territory, according to a 2018 report by the Congressional Research Service.

The gang became international as members were deported from the United States to Central America. Since 2005, law enforcement officials have estimated its membership in the U.S. around 10,000 members, contradicting suggestions that it has grown in the U.S. in recent years, the report said.

MS-13 was named a transnational gang in 2012 during the administration of President Barack Obama. The Treasury Department announced it was targeting the organization with sanctions at that time.