Six people have been arrested in connection with the killing of a 21-year-old man in Prince William County, one in a web of recent cases connected to the MS-13 gang in Northern Virginia, police said.

Several of the suspects in the death of Christian Alexander Sosa Rivas of Fairfax are MS-13 members, Prince William police said. The case also has ties to the gang-related killing of a 15-year-old girl in Fairfax County, and the disappearance and return of two other teenage girls from the same county, police said.

Three male suspects, including one juvenile, were arrested Wednesday in Pennsylvania in connection with the Rivas killing, and another man was arrested in Pennsylvania on Thursday. Two women were arrested Feb. 12 in the Baltimore area.

Rivas’s body was found along the Potomac River in Dumfries on Jan. 12, police said. They have not offered a motive in the killing.

Edgar Oswaldo Blanco Torres, 24; Jose Martir Larios Espenal, 20; Angelica Maria Blanco, 19; Keyri Sujey Portillo Gonzalez, 18; Samuel Enrique Villalobos Sanchez, 18; and an unnamed 17-year-old boy have been arrested. None of them has a fixed address.

Blanco Torres, Larios Espenal and the unnamed juvenile have been charged with murder, police said. Blanco Torres, Blanco and Portillo Gonzalez have been charged with conspiracy to commit a felony. Police said the six suspects will be extradited to Virginia.

Police declined to comment on the arrests, saying more could be forthcoming.

Fairfax County police said at a news conference last week that information that turned up during the Rivas investigation led them to conclude that a missing Maryland teenager had been killed. Her remains were found this month near an industrial park in Springfield.

Fairfax County Police Chief Edwin C. Roessler Jr. said Damaris A. Reyes Rivas, 15, of Gaithersburg, who left home in mid-December, was held against her will near an industrial park, assaulted and then killed in a “savage and brutal” fashion about Jan. 8. Her body was discovered Feb. 11 by police, just one day before the first arrests in the Rivas case.

Police said video evidence was among the clues in the killing.

Reyes Rivas’s mother told The Washington Post that her daughter had become involved with the MS-13 gang. She also said that her daughter had dated Rivas. They are not related.

The mother said her daughter had come to the United States from El Salvador in 2014. She showed The Post messages her daughter had received on Facebook, saying “those suckers want to kill you” while another added, “They have already given permission to take you out.”

Police announced last week that they had arrested 10 people, including six juveniles, in connection with Reyes Rivas’s death. Five have been charged with murder. Police have not specified a motive.

Prince William County police said that Rivas also was acquainted with Venus Lorena Romero Iraheta, 17, of ­Alexandria, who police announced last week was missing and endangered before she returned home.

Two of the adults charged in Reyes Rivas’s killing were initially arrested in another case: the disappearance of Lizzy Rivera Colindres, a 16-year-old from Springfield, reported ­missing Jan. 15. She and her 5-month-old son returned home this month.

Jay Lanham, director of the Northern Virginia Regional Gang Task Force, said the area has seen an increase in activity in MS-13 and other gangs. He said the gang has found fertile ground, recruiting among unaccompanied minors who have come across the U.S. border in record numbers in recent years. Many do not have immediate family in the area.

“These kids are certainly prime targets because of what the gangs are pitching to them in terms of belonging,” Lanham said. “They are recruiting kids down to the fifth grade,” Lanham said.

Tom Jackman contributed to this report.