San Salvador, El Salvador (CNN) -- A third migrant survived a massacre that left 72 dead in a Mexican border state, and could play a key role in authorities' investigation of the crime, El Salvador's president said.
"He is already in the United States and fortunately avoided being killed," President Mauricio Funes told reporters Sunday as the remains of 11 Salvadorans who were killed in last month's massacre were returned to their families in a somber ceremony.
A man from Ecuador, Luis Freddy Lala Pomavilla, was originally thought to be the only survivor. Lala was wounded in the attack and told authorities he played dead to fool his captors,
Last week, Ecuadorian President Rafael Correa revealed that a man from Honduras had also survived the attack. At the time, Mexican authorities said they had not revealed news of the second survivor in order to protect the person's safety.
Mexican investigators have not released information about a third survivor.
They are still in the process of identifying some of the remains of the 72 migrants killed. Officials have said the migrants hailed from Ecuador, El Salvador, Brazil, Honduras and Guatemala.
Family members in El Salvador wept Sunday as a Mexican air force plane returned the remains of their loved ones in flag-covered caskets.
Funes did not release the name of the third survivor Sunday.
"His testimony could be the key to investigating the crime, but above all, identifying those who committed it," he said.
Officials are investigating whether members of the Zetas drug cartel were responsible for the deaths.
Funes said Saturday that authorities should not only imprison whoever executed the migrants, "but also those who could have planned it."
In El Salvador, authorities have started an investigation to identify who were the Salvadorans' guides as they headed north through Mexico.
In Ecuador, authorities detained a man they say was responsible for coordinating Lala's passage to Mexico.
The growing reach of drug cartels has increased the risk for migrants crossing through Mexico to get to the United States, Mexico's National Commission for Human Rights said. An investigation by the commission showed that 9,758 migrants were abducted from September 2008 to February 2009, or about 1,600 per month.
Journalist Merlin Delcid contributed to this report.