Twenty-nine-year-old Mauricio Sanchez, of Chelsea, pleaded guilty last week to racketeering and conspiracy in connection with the Salvadoran-based gang, MS-13.

The U.S. attorney's office says this is the first such plea following sweeps earlier this year of more than 60 alleged gang members.

The racketeering plea could reinforce what many in Chelsea have suspected for some time — that Central American gangs are here, and they are organized.

In court filings, Sanchez was identified as a member of the international gang's local Eastside Loco Salvatrucha clique.

The filings also show he paid dues to gang leaders in El Salvador and in Massachusetts — money that helps fund criminal activity.

Capt. Keith Houghton, of the Chelsea Police Department, says Sanchez's plea suggests MS-13 has been making inroads here.

"It shows there is a sophistication," he says. "There is an organization, there's a structure, and I believe the investigation, through the proceedings, will indicate that."

Houghton says the federal charges also send a message to young people targeted by gang recruitment efforts.

As a member of MS-13, Sanchez admitted to stabbing a man late last year in Chelsea who he believed was a local member of the rival Central American gang, 18th Street.

After a quiet summer, Houghton says youth violence has recently picked up with the beginning of the school year.

"We did see an influx of new children arriving," Houghton says. "The new arrivals, from mostly Central America, and we try to stay on top of it as best we can if we hear rumors at the schools, working with the schools to speak directly with these kids."

Many of these children are fleeing gang violence in their home countries. Houghton says the Chelsea police want to prevent that violence from following them here.

That's why the gang dues paid by Sanchez back to MS-13 in El Salvador are particularly troubling.

Molly Baldwin is CEO and founder of Roca, a nonprofit supporting at-risk youth and young men and women.

Given the surge in numbers of unaccompanied youth from Central America, Baldwin says her group is looking for ways to better help these young people who often arrive after experiencing extreme trauma.

"We've been adapting our Chelsea site," Baldwin says, "and are in the process of slowly putting a team together to really address this group of young men who come here, want a better life, in school, out of school, back and forth, but are really having a harder time, you know, and increases their likelihood of gang violence and getting in trouble."

A spate of violent crimes over the last year in East Boston and Chelsea spurred questions in the community about increased gang activity.

Lucy Pineda is executive director of Latinos Unidos En Massachusetts, an immigration advocacy group.

Originally from El Salvador, Pineda has close ties with the local Salvadoran, Honduran and Guatemalan communities. She's heard from many concerned parents in Chelsea, some who are scared to send their children to school, afraid they could get caught up in gang recruitment.

"These kids, they fled from the country because of the problem," she says, "and they find we have the same problem in this country. And they don't want to go back to their country because they know they're going to be killed if they go back."

Pineda says she encourages people to share information about gang activity with the authorities but for some undocumented community members, the fear of deportation can outweigh the fear of gangs.