The boy fell sick and was given treatment before being found dead by Border Patrol agents.
Mario Estrada and another man, Juan Pablo Gonzalez, also conspired to kill unnamed rival candidates.
A surge of asylum seekers from El Salvador, Guatemala and Honduras have sought to enter the United States across the southern border in recent days.
In the Mexican capital, thousands of people have been evacuated.
Caravans from Central America have inflamed the debate over US immigration policy, with US President Donald Trump using the migrants to try secure backing for his plan to build a border wall on the frontier with Mexico.
The Guatemalan president's son and brother have been accused of tax fraud as a result of the commission's investigation and are awaiting trial.
President Donald Trump has made hardline immigration policies a central plank of his presidency, drawing fire from critics who accuse him of demonising migrants for political gain.
Neither the father nor other family members cast blame on US border authorities in their first statements about the tragedy.
The girl died of 'dehydration and shock'.
As the volcano's activity fell back to normal parameters, evacuees were asked for the sake of cautiousness to return home on Tuesday by bus.
A spokesman for Guatemala's disaster management agency CONRED said 2,995 residents in the municipality of Escuintla and two other districts were moved to shelters as a precaution.
The US president says a group of several thousand migrants walking through Mexico towards the US border has thrown rocks 'viciously and violently' at Mexican police.
A caravan of Central American migrants estimated to number at least 3,500 people left Honduras in mid-October and is now in southern Mexico on its way to the US border.
Trump has characterised the migrants as an 'invasion' and falsely stated they harbour terrorists and are financed in part by Democrats.
Hondurans are fleeing poverty and gang violence in their homeland.
Presiden AS berkata, bantuan kewangan bagi Guatemala, Honduras dan El Salvador dikurangkan kerana gagal menghalang rakyat mereka memasuki AS secara haram.
Several thousand Honduran migrants moved this week through Guatemala, and some were trying to cross to Mexico.
Pihak pendakwaan berkata, Roxana Baldetti mengarahkan sekumpulan pegawai dan eksekutif perniagaan menyeleweng kira-kira AS$2.5 juta daripada tabung awam negara miskin antara 2014 dan 2015.
At least 12 inmates died in a riot in July 2013 at the same prison.
Lawyers for the victims and their families say that testimonies from survivors have proven that acts of human rights violations and sexual assault were committed in Guatemala.
He also attempted to blame deaths on the body, saying that it has caused fatalities by pressuring judges to deny 5 unidentified suspects in custody proper medical treatment.
Ramirez had received death threats for her work supporting female victims of violence in western Guatemala.
Guatemala had a series of military governments in the 1970s and 1980s, and the military remains influential in politics.
Uruguay beat Mexico 4-1, while Argentina beat Guatemala 3-0.