Authorities have moved aggressively in response. A dozen people have been charged in connection with the deaths - one with first-degree murder. Ten were scooped up last Monday in a joint raid by state, county, local, and federal agents.
Hispanic gangs have operated in and around Kennett for more than a decade, as the Mexican population has swelled, but they generally keep a low profile and, for the most part, have been involved in only minor criminality. Authorities want to keep it that way.
"We stay on top of it. We're not going to let any groups ruin the lives of law-abiding citizens," said Kennett Square Mayor Matt Fetick.
He and other officials include the burgeoning Hispanic population among the law-abiding.
"When you go into the majority of these homes, you see an American flag," said Albert McCarthy, chief of police in adjoining Kennett Township. "These are people that want to demonstrate their patriotism; they don't want to be associated with gangs."
Mexican migrants began arriving here in large numbers in the 1970s to work in the mushroom industry - the 61 area farms produce nearly half the mushrooms consumed in the United States.
Most came from rural areas of Mexico and had farming backgrounds and little formal education, said Margarita Queralt Mirkil, executive director of La Comunidad Hispana, an advocacy agency for immigrants and low-income residents.
Thanks to immigration amnesties, many stayed, gaining legal residency and citizenship. Their children were often born here. From 2000 to 2010, Kennett Square's Hispanic population surged from 1,470 to 2,963, making up nearly half the residents.
Mirkil said another attraction for Mexican immigrants is that the area maintains a welcoming, inclusive atmosphere and bears no resemblance to a large city.
"They're family-oriented," she said. "They feel this is a safe place, which is what they want for their children."
While her agency regularly provides legal assistance to the Hispanic community, the bulk of it involves civil issues such as workers' compensation or immigration.
"With the exception of an occasional DUI, we see nothing of a criminal nature," she said, adding that the topic of gangs is rarely mentioned.
The Mexican presence can be seen in Kennett Square's thriving downtown in places such as the Michoacana Grill, one of the restaurants that has made the old farming center a culinary destination.
In 2011, the borough was named one of America's 21 "Coolest Small Towns" by Budget Travel magazine.
Gang activity does not square with the idyllic picture the area seeks to present.
Kennett Square Police Chief Edward A. Zunino Jr. estimated the total gang population in the borough and surrounding areas at about 25, but associates and hangers-on can swell the number.
Most are in their late teens or 20s. Not all are Hispanic - the man accused of first-degree murder in the stabbings is named Jones.
To keep tabs on gang activity, local police forces in the area have collaborated with county, state, and federal law enforcement officials in Pennsylvania and Delaware. New Garden Township Sgt. Joseph Nangle said a regional task force started in 2004 that met monthly for several years created invaluable contacts and intelligence that facilitated the arrests in the double homicide.
"I still speak with some of those folks at least once a week," he said, adding that he believed some of the gang activity had shifted westward from Kennett to places such as Avondale and West Grove.
Authorities say the largest local Hispanic gang is the Sureños, also known as the Sur 13s, the same name as a national gang that has been linked to the Mexican Mafia, which operates in prisons.
Sur 13 is Spanish for south 13 - a reference to Southern California and the 13th letter of the alphabet, M. Authorities say they believe the M stands for marijuana in some groups, mafia in others.
Local authorities say that while local members have adopted Sureño iconography in tattoos and grafitti - a triangle of three dots or the Roman numeral 13 - any further ties are tenuous.
"There's no hierarchy," Zunino said. "A few people get together and call themselves Sureños, and they don't answer to anyone. They may be just as apt to fight with a cell of Sureños in Delaware as a rival Viking group near Kennett."
The Vikings, also known as the Vaqueros, originated in southern Chester County to protect themselves from the Sureños, according to Zunino. They sometimes combine forces with another gang, the Ochos, against the Sureños.
He said the gangs periodically made their presence known through grafitti, which is a way to mark their territory.
A couple of months ago, Sur 13 grafitti was plastered all over a bathroom at Anson B. Nixon Park in Kennett Square. Zunino said that because of the task force, his department received great cooperation from authorities in Delaware, where the gang members lived, and were able to make three arrests.
If officers see gatherings they suspect are gang-related, they will establish a presence, "which makes them [gang members] uncomfortable." Zunino said one group started meeting at a Mexican food store in Kennett Square until police began frequenting the area.
"We don't see a lot of cases where they actively seek each other out," Zunino said of the rival gangs, adding that trouble can occur when paths cross.
Zunino said younger gang members have learned not to flaunt their gang affiliation through their dress or tattoos at school because it gets the attention of officials, which they do not want.
Usually, "they're good at staying under the radar," he said.
Contact staff writer Kathleen Brady Shea at 610-696-3815, firstname.lastname@example.org, or @brandywinebits on Twitter. Read her blog, "Chester County Inbox," at www.philly.com/chescoinbox