A fourth hiker, Son Mockfessel, had made the fateful decision to stay at the hotel because of a cold.
As his friends were being apprehended, Mockfessel received an urgent phone call from them, saying, "We're surrounded."
At the time of their arrest, Iran's state TV said that the Americans were arrested for "illegal entry into Iran from Iraq's Kurdistan region."
Iranian authorities said the hikers ignored warnings from Iranian guards.
The fate of the three Americans may have been complicated by a report by the Iranian Fars News Agency quoting an Iraqi police commander, Anwar Haji Omar, as saying that the captured Americans are CIA agents.
A State Department official called the spying suggestion ridiculous.
In early August, the hikers were moved to Tehran and the Iranian foreign ministry blocked Swiss diplomatic efforts being made on behalf of the United States, refusing to allow consular access to the hikers or even to disclose their location.
Throughout the ordeal, family and friends have remained optimistic, creating a Web site to tell the story of Bauer, Shourd and Fattal and to keep the world informed of their situation.
"Every day when I wake up, it's the first thing I think about, but nothing yet," Shannon Bauer told "Good Morning America" last month.
The arrests prompted comparisons to the two U.S. journalists, Euna Lee and Laura Ling, captured by North Korea earlier this year after walking across the border from China. It also comes on the heels of the detention of U.S. journalist Roxana Saberi earlier this year. Saberi was accused of spying but was later released.
As with Saberi's case, this incident highlights the troublesome relationship between Iran and the United States. The two countries haven't had diplomatic ties in the past 30 years and while President Barack Obama has said his administration is open to talks with his counterpart, Ahmadinejad, the relationship has yet to progress.
In July, Iran's outspoken leader pointed the finger at the West and the U.S. government for fomenting unrest following its contested election, which created a series of violent protests and clashes. Iran has also accused the United States of fostering unrest in Iranian Kurdistan, just across the border from northern Iraq.
Some say that the hikers' arrest and accusations of spying are clear indications of Iranian attitude to the United States.
"How the Iranians treat them is going to be a message to President Obama and the U.S.," Elliot Abrams, a senior fellow at the Council on Foreign Relations, told ABC News last month. "If they start talking about spying and start talking about needing to investigate and this thing runs into days and then weeks, that's a very serious message that they don't want better relations with us."