WASHINGTON — A leader of a notorious street gang responsible for abducting 17 people tied to an American-based missionary group in Haiti last year was indicted by a federal grand jury on Tuesday on charges of conspiracy to commit hostage taking, prosecutors said.

Joly Germine, also known as Yonyon, was a top member of the 400 Mawozo gang when it captured volunteers with Christian Aid Ministries, based in Ohio, in October, according to the indictment. The missionaries, 16 Americans and one Canadian, were seized as they were returning from a visit to an orphanage in Ganthier, near the capital of Port-au-Prince.

Mr. Germine, 29, was extradited to the United States last week after being held by the Haitian National Police. Mr. Germine, who was previously charged with firearms trafficking in a separate case, will appear in Federal District Court for the District of Columbia on Wednesday. The charges in the hostage-taking case are related to the abductions of the 16 American missionaries, the Justice Department said.

Other leaders of the gang, including Wilson Joseph, and others directly involved in the abduction, remain at large.

The missionaries — including five children — were either freed or managed to escape, mostly unharmed, in late 2021, after being held for several months under the constant threat of violence.

The gang, emboldened in the chaotic aftermath of the assassination of President Jovenel Moïse that July, had demanded $1 million per hostage in the days after the kidnapping.

Prosecutors said that Mr. Germine, who was in a Haitian prison at the time of the abduction, “directed and asserted control of 400 Mawozo gang members’ kidnapping operations.”

Mr. Germine oversaw negotiations for the release of the missionaries, who were in the country to help rebuild roads, install water systems and repair houses after an earthquake, Justice Department officials said.

One of the gang’s other goals in abducting the missionaries was to secure Mr. Germine’s release, prosecutors said.

“This case shows that the Justice Department will be relentless in our efforts to track down anyone who kidnaps a U.S. citizen abroad,” Attorney General Merrick B. Garland said in a statement. “We will utilize the full reach of our law enforcement authorities to hold accountable anyone responsible for undermining the safety of Americans anywhere in the world.”

The indictment was also intended to dissuade other groups from attacking Americans who were “volunteering their services” in Haiti and other poor countries, said the U.S. attorney for the District of Columbia, Matthew M. Graves, whose office is prosecuting the case.

Members of 400 Mawozo are known for their violent confrontations with other local gangs, but in this case, they did not seriously injure their captives, perhaps because they valued the volunteers as bargaining chips.

Two of the hostages were released in November, three more were freed in early December and the rest escaped about a week later, evading their pursuers by hiding in dense brush and using the stars to guide their route.

After they were released, the missionaries offered “forgiveness” to the gang members if they repented for their sins, according to a statement posted on the aid group’s website.

The ministry did not immediately return a request for comment late Tuesday.

Haiti’s gangs have rampaged, largely unchecked, since Mr. Moïse’s killing, controlling vast sections of the capital, countryside and major routes, including the main road leading to Ganthier.

The 400 Mawozo gang, which operates east of the capital, is one of Haiti’s most dangerous. It has been implicated in a range of crimes, like seizing Haitians and foreigners en masse from cars and buses. It is also believed to have killed a famous sculptor, according to local news accounts.

Their name is an inside joke. It means “400 simpletons” in Creole.

About 1,200 people, 81 of them from abroad, were abducted last year, according to the Center for Analysis and Research in Human Rights, a nonprofit group in Port-au-Prince.

Last week, an agricultural official from the Dominican Republic was kidnapped, then released, while driving from the capital to the Dominican border town of Jimaní.

Dominican officials believe the 400 Mawozo gang was behind that abduction, too.

At least 20 people were killed in street clashes between 400 Mawozo members and a rival gang, Chen Mechan, in Cité Soleil, one of Port-au-Prince’s most impoverished and violent neighborhoods.