Otto Warmbier appeared emotional at a news conference a month later, in which he tearfully confessed to trying to take the sign as a “trophy” for a US church, adding “the aim of my task was to harm the motivation and work ethic of the Korean people”.
Foreign detainees in North Korea have previously recanted confessions, saying they were made under pressure.
His parents Fred and Cindy told CNN in early May that they had had no contact with their son for more than a year.
In a statement, Fred and Cindy Warmbier said: “Otto has left North Korea. He is on a Medivac flight on his way home.
“Sadly, he is in a coma and we have been told he has been in that condition since March 2016. We learned of this only one week ago.”
They were quoted by the Washington Post as saying they had been told their son had contracted botulism, a rare illness that causes paralysis, soon after his trial in March 2016.
Otto Warmbier was given a sleeping pill and had been in a coma ever since, the newspaper said.
Rex Tillerson made no mention of Otto Warmbier’s condition in his statement, saying only that he was on his way home to be reunited with his family and would not make any further comment, out of respect for the privacy of the family.
The US has in the past accused North Korea of detaining its citizens to use them as pawns in negotiations over its nuclear weapons program.
The arrests have come at a time of heightened tension between North Korea and the US and its regional neighbors.
Dennis Rodman is a friend of North Korean leader Kim Jong-un and has made several visits to the country in recent years.
There was some speculation that Dennis Rodman might plead the case for the American detainees, but en route to North Korea the basketball star told reporters “my purpose is to actually see if I can keep bringing sports to North Korea”.
A number of long-forgotten deadly microbes have been uncovered in the National Institutes of Health (NIH) laboratories in recent weeks, including the deadly toxin ricin and the bacteria that cause plague.
The highly poisonous substances were found in a hunt triggered by the accidental discovery in July of vials of smallpox at a lab near Washington.
They included vials of ricin and pathogens that cause botulism, the plague and a rare tropical infection.
The substances, some dating from nearly a century ago, have now been destroyed.
Officials from the NIH said some of its laboratories were cleared to use poisonous substances and were checked regularly.
A number of long-forgotten deadly microbes have been uncovered in the NIH laboratories in recent weeks
However, the recent finds were from historical collections that were once allowed to be stored without regulation.
They included a bottle of ricin, a highly poisonous toxin, found in a box with microbes thought to be 85 to 100 years old.
“NIH takes this matter very seriously. The finding of these agents highlights the need for constant vigilance in monitoring laboratory materials in compliance with federal regulations on biosafety,” a memo from the agency said.
The authorities said the newly discovered toxins had been improperly stored but were in sealed containers and no employees were in danger of infection.
The search for unregulated toxic substances was initiated after the discovery of long-forgotten vials of smallpox in July.
The virus, believed dead, was located in six freeze-dried and sealed vials. It was said to be the first time unaccounted-for smallpox has been discovered in the US.
The smallpox disease was officially declared eradicated in the 1980s.
New Zealand dairy firm Fonterra has apologized for the distress caused to parents because of a scare over contaminated products.
Fonterra CEO Theo Spierings was speaking in China after it emerged on Saturday that batches of whey protein contained bacteria that can cause botulism.
Contaminated products, including infant formula, were exported to a number of countries, including China.
Botulism is an extremely dangerous form of food poisoning.
“We regret the distress and anxiety which this issue could have caused,” Theo Spierings told reporters in Beijing.
“Parents have the right to know that infant nutrition and other products are safe.”
Theo Spierings added that Fonterra was committed to China and was working with regulators to address the problem.
China and Russia have moved to ban imports of the contaminated products.
Fonterra said it had received confirmation that China had not imposed a blanket ban on its products.
Fonterra has apologized for the distress caused to parents because of a scare over contaminated products
Earlier on Monday, New Zealand PM John Key questioned why Fonterra, the world’s largest dairy exporter, delayed raising the alarm over the contaminated products.
John Key said concerns were raised after a series of tests in May 2012.
“When you’ve got a company that’s our largest company, our largest brand, our largest exporter that is the flagship for New Zealand and your whole business is about food safety and food quality you think they’d take such a precautionary view to these things and say if it’s testing for some reason in an odd way that it would just be discarded until they were absolutely sure that its right,” John Key said.
However, Theo Spierings addressed this by saying that the first sign of a problem only came to light after tests in March this year.
Fonterra said the bacteria came from a dirty pipe at a processing plant for whey protein concentrate.
It said the bacteria had been found in three batches of whey protein which had been used in Nutricia Karicare for infants.
Fonterra has exported the contaminated whey protein concentrate to China, Malaysia, Vietnam, Thailand and Saudi Arabia.
So far, there have not been any illnesses reported related to the contaminated products.
China relies heavily on New Zealand for its imports of milk powder. The country experienced a tainted milk scandal in 2008 that killed six babies and made about 300,000 ill.
According to Chinese state media, nearly 80% of dairy products imported by China come from New Zealand.
New Zealand is the world’s largest dairy exporter.