Hector Alejandro Cabrera Fuentes, 34, was wearing a tan jumpsuit and was shackled by hands and feet during the proceeding. He had a scruffy beard and appeared relaxed.
During the short hearing, US Magistrate Judge Chris McAliley explained Fuentes' rights to a bond hearing. Fuentes' temporary attorney, federal public defender Bonnie Phillips Williams, said that she has been in contact with his family who needs more time to hire an attorney.
"We do expect that you are financially able to retain an attorney," McAliley said.
Fuentes agreed with the judge and replied in English, saying that while his contract as an occupational researcher in Singapore has now ended, he plans to use his savings to hire an attorney and post bond.
"Thank you, your honor," Fuentes said to the judge as the hearing came to an end. His arraignment is scheduled for March 3 and he maintains the right to a bond hearing. He is currently in the federal detention center in Miami, according to Bureau of Prison records.
'We can help each other'
Fuentes is charged with acting as a Russian agent within the United States without notifying the government and one charge of conspiracy to do the same.
Fuentes traveled to Miami from Mexico City on February 13. The next day, he was allegedly spotted by a security guard where the US government source lives and his female companion was observed photographing the license plate of the US source.
Fuentes believed the Russian official worked for the Federal Security Service, Russia's counterintelligence agency which reports directly to Vladimir Putin, according to the criminal complaint.
At one point last year, the Russian official told Fuentes "we can help each other," the complaint says.
A published author in scholarly journals
The internet and social media are peppered with photos and interviews of Fuentes talking about his work as a scientist in Mexico, Russia, Germany and Singapore.
Fuentes is listed as the author or co-author of dozens of peer-reviewed journal articles about cardiovascular issues dating back eight years. The most recent one was published last month.
"You're going to return from Russia like a popsicle," Fuentes remembered his father joked with him at the time.
While the language and cultural barriers were his first hurdles, Fuentes said that after finishing a semester of preparatory school in Russia, he began working toward his microbiology degree in Russia. He went on to earn a master's degree at Kazan State University in Russia, Fuentes said.
His LinkedIn profile lists him as a doctoral student and a post-doctoral research associate at Justus-Liebig-University in Giessen, Germany.
During the radio interview, Fuentes mentioned having a wife and a daughter. But court documents say he has two wives, one from Mexico and one from Russia. According to the court documents, the Russian woman has two daughters.
'Innocent until proven guilty'
CNN talked by phone to one of Fuentes' friends, Armando Toledo, 56, from the small Mexican town of El Espina. Toledo said he is only aware that Fuentes is married to a Mexican woman and that he has two daughters.
Toledo said he is surprised by his friend's arrest and described receiving the news akin to being hit by a bucket of cold water. He said that the Fuentes he knows is dedicated to medicine and his community.
Fuentes, Toledo said, helped people with supplies to rebuild their homes after the 2017 Mexico earthquake, and is working on a health, technology, cultural and medical project that was expected to benefit several southern Mexican states and has inspired Mexican youth to study the sciences.
Fuentes is not the only person from his small Mexican town to study in Russia, according to Toledo. At least two or three other students have done the same.
Toledo said he thinks the allegations against Fuentes are speculation.
"Everyone is innocent until proven guilty," Toledo said.