Federal authorities have arrested a Mexican citizen on charges that he collected information about a U.S. government informant on behalf of Russia.

Hector Alejandro Cabrera Fuentes, 34, first aroused suspicion on Friday when he followed another vehicle into the Miami-area condominium complex where the informant lived, according to a newly unsealed federal complaint. As a security guard approached Fuentes’s rental car, his wife got out of the vehicle and took a picture of the informant’s license plate.

U.S. prosecutors claim he was carrying out orders from a Russian official who had recruited him with promises of helping his family. A Singapore resident and researcher at the country’s National Heart Center, Fuentes made several trips to Moscow to meet with the official, who directed him to rent a specific property in Miami-Dade County and report back to Russia the license plate and location of the informant’s car.

“The Russian official told Fuentes not to rent the apartment in Fuentes’s own name and not to tell his family about their meetings,” a Justice Department news release said.

Court records in the case, which was first reported by the Miami Herald, were filed under seal Tuesday and unsealed Wednesday. The complaint identifies the target of Fuentes’s surveillance as a confidential informant “who previously provided information regarding [Russian Intelligence Service] activities” that had national security implications for the U.S.

When the security guard stopped him Friday at a parking garage in the informant’s housing complex, Fuentes named someone he claimed to be visiting. The guard did not recognize the person as living there and told Fuentes and his wife, who was not named in the complaint, to leave the property.

Two days later, the couple was intercepted after arriving at Miami International Airport for a flight to Mexico City, federal prosecutors said. Customs and Border Protection inspected the wife’s phone and discovered “a close-up image of the license plate” in a folder of recently deleted photographs. Fuentes admitted telling her to take the picture. A search of his phone found that she had sent the photo to him using WhatsApp and that he had been communicating with the Russian official.

During an interview with FBI agents on Monday, according to the complaint, Fuentes described having repeated contact with a person he believed worked for the Russian government. He said that in addition to the wife who was traveling with him in Miami, he had a Russian wife who had been prevented from leaving Russia with her two daughters since March.

Fuentes told the FBI agents that he was contacted by the Russian official in May, while visiting his family in Russia. The official asked for a meeting in Moscow, saying that he had met Fuentes during previous professional meetings and exchanges. Fuentes agreed, and recognized the official from their past encounters. The official told him his family "should not go to Europe or obtain U.S. visas,” the complaint said. That comment, and the exchanges that followed, led Fuentes to believe the man worked for the government.

Sometime in June or July, the complaint said, the two met again in Moscow. The official told Fuentes that he knew he had been looking for real estate in Miami, showing him a “hardcopy printout of Fuentes’s historical Gmail account.” Fuentes said the printout was from 2015, when he “was indeed looking for real estate in the Miami area.”

“In the same conversation, the Russian Official brought up Fuentes’s family’s inability to depart Russia and told Fuentes that ‘we can help each other,’” the complaint said.

In December, Fuentes rented the apartment the official directed him to, which was located in the same condominium complex that was home to the informant. It was during a February trip to Moscow that he was directed to collect the information on the informant’s car. The official instructed him not to take any photos. Fuentes told the FBI agents he did so anyway “out of convenience.”

He said he was set to meet the Russian official in April or May to fill him in on the search for the informant’s vehicle.

Fuentes is charged with acting as an agent of a foreign government without notifying U.S. officials. During a brief court hearing on Tuesday, the Miami Herald reported, he told a judge that he would have difficulty accessing money to pay for a defense attorney.

“None of my family knows I’m here,” he said, according to the newspaper.

On Wednesday, Fuentes remained at the Federal Detention Center in Miami, Federal Bureau of Prison records show. He was set to appear back in court Thursday for a pretrial detention hearing.

Read more: