The 17-year-old from Sterling was gunned down as he walked to a bus stop. The 22-year-old from Montgomery Village was shot ­execution-style in the woods. The 22-year-old from Herndon was butchered with knives and a machete in a park.

Authorities say the three killings this year were brutal, brazen and targeted, a continuation of a new wave of violence by members of the region’s biggest and most notorious gang: MS-13.

In 2014, FBI officials noted an upswing in violence by the gang after years of relative quiet. They attributed the resurgence to gang leaders in El Salvador attempting to reconstitute operations here in order to make more money.

The gang’s leadership had been decimated and many members had been put in jail following a string of high-profile machete attacks and killings that focused law enforcement attention on MS-13 between the late 1990s and mid-to-late 2000s. In Maryland alone, the U.S attorney’s office secured 42 convictions of alleged gang members as of 2009, according to the U.S. Justice Department.

Law enforcement officials said MS-13’s drive to renew itself is spurring the latest round of killings. Many of the alleged perpetrators and victims are in their teens or early 20s.

“MS-13 appears to be making a push for recruitment, once again reverting to their old tactics of violence and intimidation,” Douglas Keen, chairman of the Northern Virginia Regional Gang Task Force, wrote in an e-mail.

Those grisly tactics were on display this past week in Fairfax County General District Court, where an 18-year-old Sterling man had a preliminary hearing in the killing of 22-year-old William Adolfo ­Rivas Leiva at Herndon’s Folly Lick Park in March.

Herndon Police Sgt. Claudio Saa testified that the defendant, Moises Dominguez, confessed that he, Leiva and four other associates of MS-13 went to the park on the pretense of smoking marijuana. At the time, Saa testified, Dominguez was not a full-fledged member of the gang.

As they got to a wooded area, Saa said, the gang members began violently slashing Leiva with knives and a machete. Saa testified that Dominguez told him a knife was eventually passed to him and he began stabbing Leiva in the side. Saa said Dominguez told him Leiva was already lying on the ground at that point.

Saa testified that after participating in the killing, Dominguez was “deemed a member” of MS-13. Saa did not discuss the motivation for the killing in court, but police wrote in a search warrant that Leiva was killed because he was trying to leave MS-13.

Leiva’s slaying was similar to the killing of Roberto Cruz, 22, in a wooded area of Gaithersburg on Nov. 1.

“Get on your knees,” one of his assailants allegedly told him, according to a police search warrant filed in court, “and if you don’t, we will make you get on your knees.”

Cruz tried to protect himself with his phone. “I know what’s happening, and I am recording you guys,” he allegedly said.

Several shots were fired, hitting Cruz in the face, neck and shoulder.

“It was an execution-style murder,” Montgomery prosecutor Christina Rodriguez later said in court.

Police have arrested three suspects in the case: Luis F. Avelar Morales, 17, Daniel Adonai ­Ramos, 19, and Juan Espinal ­Rapalo, 18, all of the Gaithersburg area. In court papers, detectives specifically allege that Morales and Ramos said they were MS-13 members and that Ramos told detectives he shot Cruz “on behalf of” MS-13. The three assailants, according to Montgomery police, thought Cruz was a member of 18th Street, a longtime rival gang of MS-13.

Bad blood between the victim, Cruz, and one of the suspects, Espinal Rapalo, appears to have been brewing. On Oct. 20, as Cruz was walking home from a restaurant, he was attacked and robbed by three assailants, including ­Espinal Rapalo, according to police. Eleven days later, Cruz was found shot to death.

Capt. Paul Liquorie, director of the Montgomery County Police Department’s Special Investigations division, said detectives are trying to determine whether Cruz was a member of the 18th Street gang or if those responsible for his killing just thought he was. In any case, he said, “this appears to be a continuing MS-13 versus 18th Street targeting.”

More broadly, Montgomery police are seeing an uptick in the percentage of street crimes committed by MS-13 members, ­Liquorie said. Many of the crimes are strong-armed robberies or assaults, in which MS-13 members approach someone they suspect is in a rival gang. They examine their potential target’s tattoos and start asking questions.

“Who are you with? Who are you running with?” they ask, typically in Spanish, Liquorie said.

In the third killing, a 17-year-old who had fled poverty and violence in his native El Salvador was shot twice in the back in September as he walked to a school bus stop in the Sterling area, authorities said. They said a 17-year-old, who has not been identified because he is a minor, fired the shots that killed Danny Centeno-Miranda. Authorities said they believe the teen had ties to MS-13.

Henry Dominguez Vasquez, 20, and Juan Aguirre Zelaya, 18, were also arrested and charged with being accessories to the shooting and with possession of a firearm while in the country illegally. It was unclear whether authorities believe Vasquez and Zelaya were linked to the gang.

Centeno-Miranda’s case has drawn the attention of Sen. Charles E. Grassley (R-Iowa), since the alleged killers appear to have ties to MS-13 and entered the country during the recent waves of unaccompanied minors crossing the Texas border. In a letter to the Department of Homeland Security seeking answers about the case, Grassley wrote that the perpetrators appeared to be part of the Unaccompanied Alien Children Program, had failed to appear for immigration hearings and were marked for deportation.

“This tragedy appears to be yet another example of problems in the vetting of unaccompanied minors,” Grassley said in a statement. “In this case, minors with possible gang ties were allowed to go off the grid after entering the country illegally. And when their court dates finally arrived years later, they were nowhere to be found.”

The latest killings are all the more troubling because they come on the heels of major federal indictments in Maryland and Virginia last year that swept up 21 alleged gang members in connection with eight killings and one attempted murder.

“They want to replenish their numbers, and they’re playing hardball,” said Montgomery County’s top prosecutor, John McCarthy.