A United States federal judge has ordered 5-year-old Liam Conejo Ramos and his father, Adrian Alexander Conejo Arias, to be released from federal immigration custody after the pair were detained in their driveway in Minnesota last week.

The detention sparked outrage nationwide and protests at the family detention centre in Dilley, Texas, where they have been held.

In a sharply worded statement, US District Judge Fred Biery said the administrative warrants issued by the executive branch to its own agents “do not pass probable cause muster”.

“That is called the fox guarding the henhouse,” he wrote. “The Constitution requires an independent judicial officer.”

Below his signature, the judge also included the now well-known photo of Ramos as he was taken into custody wearing a Spider-Man backpack and a bright blue hat.

The photo and Liam’s detainment further inflamed tensions between Minnesota residents and the Trump Administration’s immigration enforcement efforts there.

The Justice Department did not immediately respond to a request for comment. The judge ordered that Liam and his father be released from custody “as soon as practicable”, and no later than Wednesday (NZT).

“Ultimately, Petitioners may, because of the arcane United States immigration system, return to their home country, involuntarily or by self-deportation,” Biery wrote.

“But that result should occur through a more orderly and humane policy than currently in place.”

Liam was returning from preschool when he and his father were approached by Immigration and Customs Enforcement officers, according to the boy’s school district, Columbia Heights Public Schools.

The Department of Homeland Security said Arias fled on foot and was pursued by several ICE officers, while another officer remained with Liam for his safety.

An adult who was living in the home but outside at the time of the incident “begged the agents” to leave Liam with them, but ICE agents refused, the school district said.

DHS said it was not targeting Liam and that ICE’s policy is to ask parents if they want to be removed with their children, or ICE will place the children with a safe person designated by a parent.

It was not clear why ICE officers had not left Liam in the care of the adult whom school officials say had begged officers to leave Liam there.

The family’s lawyer, Marc Prokosch, said in a previous statement that Liam and his father are not US citizens but “have been following the legal process perfectly, from presenting themselves at the border to applying for asylum and waiting for the process to go through”.

Biery, who was appointed by President Bill Clinton, cited lines from the US Declaration of Independence and the Fourth Amendment in his justification of Liam’s and his father’s release.

He said the case “has its genesis in the ill-conceived and incompetently implemented government pursuit of daily deportation quotas, apparently even if it requires traumatising children”.

He wrote: “Observing human behaviour confirms that for some among us, the perfidious lust for unbridled power and the imposition of cruelty in its quest know no bounds and are bereft of human decency. And the rule of law be damned.”