Easy. In order to make a citizen's arrest in Arizona a person must have witnessed the misdemeanor. These clowns were 10 miles from the border, and unless Superman loaned them his X-ray eyeballs, there is no chance they actually witnessed any crime except their own felonies of aggravated assault and false imprisonment.
When you go into a gas-station and rob the clerk, you are committing a crime. When you leave and drive down the street, you are no longer committing a crime. When you cross into the U.S. illegally, you are committing a crime. When you drive down the street afterwards, you are still committing a crime - since it is your prescence within the borders that is the crime.
If the people were here illegally, then the people making the arrest were, in fact, witnessing the crime. The main issue is - they'd better be right, and they'd better not use excessive force.
From the story above: "Dumas was charged with six counts of aggravated assault and five counts of unlawful imprisonment following the early morning July 31 incident where deputies said he and Matthew Paul Hoffman, arrested on the same charges on Monday, detained a group of six illegal immigrants that had just entered the United States through the Colorado River.
How big is that river anyway? BTW, they would have had to have used Superman's telescopic vision, not X-ray vision.;-)
I will agree with your "temporary worker" (Bracero Program) if, and only if, all illegals are deported first, then reprocessed for this privilege.