Five foreign men were arrested during a courthouse break-in early on Wednesday and police said they found photographs of public buildings, water systems and malls from various U.S. cities in their van.
The men, at least three of whom were in their 20s, will be questioned by a joint terrorism task force including the FBI and immigration authorities, officials said.
Bexar County spokeswoman Laura Jesse said three men were found inside the 120-year-old Bexar County Courthouse, a landmark in downtown San Antonio and two in a large recreational vehicle parked in front of the building.
She said all five were Moroccans.
Inside the RV, officials say they found "photographs of infrastructure" including shopping malls, water systems, courthouses and other public buildings that they say were taken in cities across the United States.
"They got travel documents, parking passes, they have been all over the country," Police Captain Cris Andersen said.
"A lot of photographic equipment, a lot of documentation equipment (was) inside their vehicle."
"They are going to be held for interrogation by the FBI, Immigration and Customs Enforcement, and the joint terrorism task force," Andersen said.
San Antonio is home to three major military bases, and officials have notified them of the incident, and have told them to be on the lookout for any suspicious activity and vehicles.
A military intelligence convention is underway at the city's Convention Center several blocks away, with top intelligence officials including White House officials set to speak, but investigators didn't say whether there was any connection.