"The Hunt with John Wash" returns Sunday, July 12 at 9 p.m. ET/PT on CNN. Got a tip? Call 1-866-THE-HUNT (In Mexico: 0188000990546) or click here.
(CNN)This story was originally reported August 17, 2014.
On October 14, 2002, B.J. Schany was busy at work filling dozens of rail cars full of corn from a grain elevator in Denison, Iowa. When he went to open the lids on the second set of rail cars, he came across a grisly discovery.
"The rail car was locked, I remember unlatching the lock on the top hatch," Schany recalled. "I've done that hundreds if not thousands of times before and never, never ever had anything close to something like this happen."
Guillermo Madrigal Ballesteros, 56
- Accused of organizing the transport of illegal immigrants
- On the run since 2003
- Could be in Mexico or Texas
Inside that rail car were the decomposed bodies of 11 men and women. An examination of the remains later determined that all had died of dehydration and hyperthermia. The rail cars had originated in Mexico before making the journey to a storage facility in Oklahoma where they sat for four months, according to Tom Hogan, former sheriff of Crawford County, Iowa.
"Whatever had transpired there had transpired months prior to coming to Denison," Hogan said. "We were pretty sure we were dealing with someone trying to enter the United States illegally."
Hogan said investigators believed the 11 men and women had "probably entered the railroad car on their own free will but then someone had closed the latch and locked it so that it couldn't be opened."
"It didn't look like a murder in the traditional sense," Hogan said. Nevertheless, that's what the evidence was beginning to indicate.
Documents inside the rail car identified the people as nationals of Mexico, Honduras, and Guatemala, according to Alonzo Martinez, a former district director with Immigration and Naturalization Service who worked on the case.
"Somebody was responsible for these 11 people who perished inside this car, and we were looking for somebody that we were going to hold accountable," Martinez said.
Investigators got a big break when Eliseo Acevedo reached out to INS, looking to find his missing brother.
"He was afraid that one of those bodies was going to be his brother," Martinez said. "Eliseo told us that he was living in New York when his younger brother called him to tell him that he was in Harlingen (Texas) and he needed money to pay the smugglers."
Eliseo Acevedo -- a Guatemalan immigrant who lives in Katonah, New York -- agreed to pay $300 to get his 18-year-old brother to Houston.
"I said to him, if you're going to make the next move, don't put yourself in any danger," Acevedo said. "My hopes were that he would call me from Houston and tell me 'I'm here.' "
That never happened. Byron Acevedo was identified as one of the 11 bodies inside the train car.
After the news had spread about the grisly discovery in Denison, Iowa, Acevedo received a phone call from a man who identified himself as "Memo" who told him he had nothing to do with his brother's death.
"During this phone conversation, he also told him the composition of the group," Martinez said. "He said there would be four women and seven men, and we found that quite interesting."
That's because the gender breakdown of the so-called "Denison 11" had not been publicly released.
Investigators identified "Memo" as Guillermo Madrigal Ballesteros, a Mexican national based in Mexico City who is accused of helping to smuggle people from Central America into the United States through Mexico between January 2000 and February 2003 -- including these 11 men and women. Martinez described Madrigal -- who goes by "Memo" or "Don Memo" -- as "one of the main operators of this smuggling operation."
At the time, authorities didn't have any photos or identification for Madrigal, although they had been tracking him and other members of the alleged smuggling ring, according to retired anti-smuggling agent Gabe Bustamante.
"I decided we needed to identify him," Bustamante said. "We called the Harlingen police department, they were able to pull him over on a traffic violation."
They took him into the station and took a couple of photographs. Bustamante alerted Martinez who asked the federal prosecutor to proceed with charges against Madrigal in relation to the smuggling operation. But the assistant U.S. attorney said it was too early.
"As hard as it was, we had to tell the police department to let him walk," Martinez said.
More than a decade after the immigrants' deaths, federal authorities decided last summer to dismiss the case against Madrigal without prejudice, meaning it can be reopened if he's arrested. Assistant U.S. Attorney Michael Wynne explained that keeping the case open became a burden for Homeland Security, saying they were liable for keeping people who would otherwise be undocumented immigrants in this country indefinitely as potential witnesses for a trial that likely would never occur. Wynne says there's reason to believe that Madrigal may be in Texas and possibly involved in the illegal transport of immigrants. That brings a new sense of urgency to the efforts to apprehend him, Wynne said.
"Nothing can bring my brother back but I think the responsible people ... should have been arrested now and in jail," said Eliseo Acevedo.