When the mother was unable to keep up with the group, the smugglers reportedly left her behind.
It wasn't until noon the next day the county Sheriff's Office alerted the Border Patrol to a group of illegal border crossers who were in distress.
Agents found a group of six immigrants, and later — with the help of a helicopter — found the woman, who had already died from heat exposure.
Lopez was arrested in May in connection with the death of another woman, who had been led across the border by those associated with a smuggling organization.
The identity of that woman was unavailable Saturday.
Lopez brought the woman to the Gold Cross Ambulance Service facility in El Centro for medical attention.
An investigation by the El Centro Sector Border Patrol Anti-Smuggling Unit revealed Lopez was reportedly part of the smuggling operation.
According to reports, Lopez was sent by the organization to pick up the woman after another unidentified smuggler left her behind because she was unable to keep up with the group with whom she had crossed the border.
Temperatures in the desert that day exceeded 111 degrees and the woman died from heat exposure and dehydration.
Border Patrol officials said the fact that three men were taken into custody and pleaded to the charges against them sends an important message to smuggling operations that they will be prosecuted to the full extent of the law.
Kerry Anderson, assistant chief of the El Centro Sector, said hopefully undocumented immigrants will get the message that they shouldn't put their lives at risk and they shouldn't trust immigrant smugglers.
He said the smugglers are interested in little else but their profits and consider immigrants as nothing but human cargo.
During the last fiscal year, from Sept. 1, 2000, to Oct. 31, the local Border Patrol saw more immigrant deaths occur that at any time in the past.
Some 95 deaths were recorded, including those who died as a result of heat exposure, from drowning and in traffic accidents.
In past interviews, Border Patrol officials have said they know the immigrants will keep coming and the smugglers will continue their efforts.
In the past year, officials have said, they saw an increase in efforts to prosecute smugglers and that effort will continue.
Officials also are hopeful this year, with realignments to the coverage area and expanded search and rescue efforts, the number of deaths will decrease.
"We are trying to do everything in our power to cut down on the injuries and deaths," Anderson said. "We are not going to stay stagnant. We are going to change things to try to be more effective."
>> Staff Writer Darren Simon can be reached at 337-4082.