A third man, 23-year-old Alexander Batista-Polanco, pleaded guilty days before the trial began last week and testified as the prosecution’s star witness.
Police said the group fatally shot 50-year-old Mendez when he and his partner tried to stop a car break-in at the airport. Mendez’s partner was injured.
Authorities also said a fourth man, Jesus Herman Madera Duran, was part of the group and died after being struck by gunfire.
Defense attorneys argued prosecutors failed to prove the group was at the scene and noted the absence of surveillance cameras.
Prosecutors presented cell phone and DNA evidence they said placed the defendants at the location.
Martinez-Fernandez and Pena-Fernande are expected to be sentenced later Monday. They both face life sentences.