The women, Noemi and her niece Andrea, did not have papers to enter the United States legally, so they stole across the harsh desert from Nogales, Mexico, to Arizona.
"Many, many of us are over there," said Beatriz Quezada Rincon, their cousin and a village hairdresser. "There is no money to sustain us here, so we have to go there to look for jobs. The crossing is very hard, but it is worth it."
Last week, Noemi and Andrea Quezada's children - 9-year-old Ricardo Solis Quezada Jr., 10-year-old Alexis Espejo Quezada and 9-year-old Lucero Solis Quezada - were found dead in their Northwest Baltimore home, one decapitated and two nearly beheaded.
Family members in Mexico say that the women, like so many before them, took their children to the United States to improve their lives and give them better educational opportunities.
It is impossible to know how many people like the Quezadas slip through the border or how many of those caught tried to cross again and succeeded.
But the flood of Mexicans trying to enter the country illegally continues. Last year, border patrol agents intercepted almost a million people crossing, according to Mario Villarreal, spokesman for U.S. Customs and Border Protection.
The Sonoran desert extends well into Mexico, so many people attempting to make the journey are physically spent well before they reach the U.S. line.
Human smugglers, called coyotes, will tell their "clients" that the walk across the border takes eight to 12 hours, Villareal said, but in fact it lasts three to five days.
"It's rugged terrain, cactus, sand, brutal sun; the temperature's incredible, no shade," he said. "Unfortunately, people often succumb to the climate."
The men arrested in the killings of the Quezada children - Policarpio Espinoza, 22, and Adan Espinoza Canela, 17 - also crossed into the country by walking through the desert, according to authorities.
It was the type of handover that federal agents make regularly along the Southwest border, one they know won't stop determined crossers for long.
Sure enough, border patrol agents intercepted and returned Espinoza at least two other times that summer, according to federal officials. But eventually, Espinoza got across.
Two years later, federal officials say, Adan Espinoza Canela followed. He told federal agents this week that he, too, walked across the Arizona desert. He was never intercepted.
It is unclear how the two got from Arizona to the house in Baltimore County where they lived until their arrest last week.
Since Sept. 11, 2001, the federal government has increased its patrols along the country's border with Mexico. There are more border patrol agents than ever before - about 11,000 - and a single agency, U.S. Customs and Border Protection, working solely to monitor the nation's edges.