A court in Santiago sentenced Cristopher Quijada Villalobos for the robbery and manslaughter of Koichiro Morita.
Police say the 57-year-old died was killed by a blow to the head from Quijada, who took his wallet and cellphone during a robbery in Santiago in 2012.
ALMA says Morita was instrumental in creating the observatory on a high plateau in Chile's Atacama desert.
The sentence was announced yesterday.
ALMA searches for clues about the dawn of the cosmos, from the coldest gases and dust where galaxies are formed to the energy produced by the Big Bang.