The US government’s prosecution of a South Korean businessman accused of illegally selling technology used in aircraft and missiles to Iran was dealt a devastating blow by a federal judge. The judge ruled Friday that the authorities illegally seized the businessman’s computer at Los Angeles International Airport as he was to board a flight home.

The authorities who were investigating Jae Shik Kim exercised the border exception rule that allows the authorities to seize and search goods and people—without court warrants—along the border and at airport international terminals. US District Court judge Amy Berman Jackson of the District of Columbia noted that the Supreme Court has never directly addressed the issue of warrantless computer searches at an international border crossing, but she ruled (PDF) the government used Kim’s flight home as an illegal pretext to seize his computer. Authorities then shipped it 150 miles south to San Diego where the hard drive was copied and examined for weeks, but the judge said the initial seizure “surely cannot be justified.”

After considering all of the facts and authorities set forth above, then, the Court finds, under the totality of the unique circumstances of this case, that the imaging and search of the entire contents of Kim’s laptop, aided by specialized forensic software, for a period of unlimited duration and an examination of unlimited scope, for the purpose of gathering evidence in a pre-existing investigation, was supported by so little suspicion of ongoing or imminent criminal activity, and was so invasive of Kim’s privacy and so disconnected from not only the considerations underlying the breadth of the government’s authority to search at the border, but also the border itself, that it was unreasonable.

The defendant was accused of unlawfully selling Q-Flex Accelerometers—models QA-2000-10, QA-2000-20, and QA-3000—manufactured by Honeywell Aerospace. They require an export license before they can be sold from within the US. Kim was accused of selling the technology to intermediaries in China and Korea before their ultimate destination of Iran.

“The government points to its plenary authority to conduct warrantless searches at the border. It posits that a laptop computer is simply a ‘container’ that was examined pursuant to this authority, and it submits that the government’s unfettered right to search cargo at the border to protect the homeland is the beginning and end of the matter,” the judge wrote.

Evidence discovered on his computer of his alleged involvement in the conspiracy that won an indictment is now suppressed, and it cannot be used against him according to the ruling. The authorities took the man’s computer in 2012 for national security reasons but allowed him to board his flight home. The government did not comment on the decision.

Judge Berman Jackson questioned whether the border search exception should apply to laptops because they carry much more private information than, say, a briefcase. Judge Jackson cited last year’s Supreme Court case, known as Riley, in which the justices ruled unanimously that the authorities generally may not search the mobile phones of those they arrest unless they have a court warrant.

The Supreme Court said that “Modern cell phones, as a category, implicate privacy concerns far beyond those implicated by the search of a cigarette pack, a wallet, or a purse. A conclusion that inspecting the contents of an arrestee’s pockets works no substantial additional intrusion on privacy beyond the arrest itself may make sense as applied to physical items, but any extension of that reasoning to digital data has to rest on its own bottom.”

Seizing on that high court opinion, Judge Berman Jackson wrote:

Applying the Riley framework, the national security concerns that underlie the enforcement of export control regulations at the border must be balanced against the degree to which Kim’s privacy was invaded in this instance. And as was set forth above, while the immediate national security concerns were somewhat attenuated, the invasion of privacy was substantial: the agents created an identical image of Kim’s entire computer hard drive and gave themselves unlimited time to search the tens of thousands of documents, images, and emails it contained, using an extensive list of search terms, and with the assistance of two forensic software programs that organized, expedited, and facilitated the task. Based upon the testimony of both Special Agent Hamako and Special Agent Marshall, the Court concludes that wherever the Supreme Court or the Court of Appeals eventually draws the precise boundary of a routine border search, or however either Court ultimately defines a forensic – as opposed to a conventional – computer search, this search was qualitatively and quantitatively different from a routine border examination, and therefore, it was unreasonable given the paucity of grounds to suspect that criminal activity was in progress.

The American Civil Liberties Union has long maintained that the authorities invoke the border exception rule to the warrant requirement to build cases when they don’t have probable cause to get a warrant.

One such high-profile incident occurred in 2010, when the authorities detained and seized a laptop, thumb drive, and digital camera from David House at Chicago’s O’Hare Airport when he returned from a vacation in Mexico. House was an outspoken supporter of WikiLeaks leaker Chelsea Manning, who at the time was facing a court-martial for leaking classified documents to WikiLeaks. Manning is now serving 35 years for the leaks.

The Department of Homeland Security confiscated House’s gear for 49 days before it was returned after the ACLU complained. The government had waited for House’s return so it could search his digital properties. As part of a legal settlement, the government agreed to destroy copies of House’s seized data.