In an American court today, the 55-year-old will be sentenced to up to a decade in prison for lying on his US citizenship papers about his alleged role in the slayings.
Federal prosecutors are seeking the maximum prison sentence for the former second lieutenant for failing to disclose his alleged participation in the murders in the Guatemalan hamlet of Dos Erres when he applied to naturalise and are asking a judge strip him of his American citizenship.
The government is pursuing the sentence in light of "the horrific nature of the human rights offences that defendant concealed in order to obtain naturalisation," prosecutors wrote in a sentencing brief.
Sosa's trial last year on charges of making false statements and illegally obtaining US citizenship brought harrowing testimony to the federal courthouse in Riverside from former comrades and a man who survived the onslaught in Dos Erres as a young boy and recounted watching soldiers take his mother to be killed as she pleaded for her life.
The case is one of several efforts to bring to justice the alleged perpetrators of the 1982 massacre. In Guatemala, five former soldiers each have been sentenced to more than 6,000 years in prison for the killings, while a former soldier was sentenced to a decade in an American prison for lying on his citizenship forms in a case similar to Sosa's.
At least 200,000 people were killed during Guatemala's 36-year-civil war, mostly by state forces and paramilitary groups seeking to wipe out a left-wing uprising.