Prosecutors say the device was left near the base visitor center, then went undiscovered for nearly a week.
TAMPA, FL — Federal prosecutors have charged a Florida brother and sister in connection with an improvised explosive device left outside the visitor center at MacDill Air Force Base, saying the brother planted it on March 10 and the pair fled to China two days later.
Why the case matters is tied to where it happened and how long the device sat before it was found. Prosecutors say the package was placed near the entrance used by visitors at one of the nation’s most important military installations. MacDill is home to U.S. Central Command and a long list of mission partners, and authorities said the device had the potential to cause deadly harm even though it did not explode. The charges also mark a shift from an early bomb scare to a wider federal case involving explosives offenses, alleged evidence tampering and an international manhunt for the main suspect.
According to the indictments and statements made by U.S. Attorney Gregory W. Kehoe, investigators say 20-year-old Alen Zheng of Land O’Lakes placed the device near the MacDill visitor center on the evening of March 10. Minutes later, Kehoe said, someone called 911 and reported that a bomb was on the base, but did not say exactly where it was. Air Force personnel searched the installation at the time and did not find it. The package remained there until March 16, when base personnel discovered it outside the visitor center and called in federal investigators. Kehoe said the device “could have potentially been very deadly,” and authorities later moved it by helicopter in a specialized container to an FBI lab in Huntsville, Alabama, for detailed forensic testing. Officials say that testing is continuing.
Prosecutors unsealed separate indictments Wednesday against Alen Zheng and his sister, Ann Mary Zheng, 27, also of Land O’Lakes. Alen Zheng is charged with attempted damage of government property by fire or explosion, unlawful making of a destructive device and possession of an unregistered destructive device. If convicted, he faces a minimum sentence of five years and up to 40 years in federal prison. Ann Mary Zheng is charged with assisting after the fact and evidence tampering. Prosecutors say she helped her brother avoid arrest and tried to impair the federal case by altering, destroying, mutilating and concealing a 2010 black Mercedes-Benz GLK 350. She faces up to 30 years in prison if convicted on all counts, and prosecutors are also seeking forfeiture of $5,000 they describe as proceeds of the charged conduct. Authorities said she was arrested after returning to the United States from China. A federal public defender declined to comment on the charges.
Investigators said the case moved quickly once the package was found on March 16. Kehoe said agents used phone data to tie the 911 call to Alen Zheng, then matched surveillance footage to the Mercedes-Benz SUV prosecutors say was used in the trip to the base. By the time agents located the vehicle at CarMax, Kehoe said, it had already been vacuumed and cleaned. Even so, investigators said they recovered residue that matched the explosive material. Agents also searched the family home and reported finding components of an explosive device there. Prosecutors say the siblings sold the Mercedes, bought airline tickets and left for China by March 12. Ann Mary Zheng later returned to the United States and was taken into custody, while Alen Zheng remains in China. Kehoe said officials are exploring all available ways to bring him back to the United States. Authorities have not announced a motive, and Kehoe said investigators do not have immediate evidence that Alen Zheng was acting for the Chinese government or any other country.
The location has added weight to the case from the start. MacDill Air Force Base sits on Tampa’s Interbay Peninsula and serves as host to the 6th Air Refueling Wing and dozens of other military partners. The base is also home to U.S. Central Command, which oversees U.S. military operations across the Middle East, Central Asia and parts of South Asia, along with U.S. Special Operations Command. In recent days, officials have said the installation has been on heightened alert as conflict involving Iran has driven extra concern around military facilities. That context does not establish a motive in this case, and prosecutors have not said the suspects were linked to any foreign power or organized network. But it helps explain why investigators and base officials treated the incident as more than a routine bomb threat. A package left outside an ordinary gate would have drawn a major response. A device left near the visitor center of a base tied to active overseas military operations drew even more scrutiny.
The legal case is still in its early stage, and prosecutors stressed that an indictment is only a formal accusation. Both defendants are presumed innocent unless proven guilty in court. The Joint Terrorism Task Force is investigating, and Assistant U.S. Attorneys Lauren Stoia and David P. Sullivan are handling the prosecution. Ann Mary Zheng is now the only sibling in custody. Alen Zheng remains the focus of the explosives case, and federal officials have not said when he might appear in a U.S. courtroom. The FBI lab work in Alabama may shape what comes next, because officials said they are testing the device for fingerprints, DNA and other forensic evidence. That could affect future filings, plea discussions or added allegations if new evidence emerges. Authorities also have not publicly explained why Ann Mary Zheng returned to the United States after traveling with her brother, or whether any other people will face charges as the investigation continues.
The story has widened beyond the two indictments. During a Thursday news conference, Kehoe said the siblings’ mother had been detained pending deportation for overstaying her visa, though she has not been charged in the explosives case. Officials also noted that another man was separately arrested this week on charges of making threatening phone calls to MacDill days after the device was found. Investigators have not tied that caller to the Zheng case. Even so, the separate threat added to the tension around the base as roads were blocked, personnel responded to alerts and national attention turned to Tampa. The image that remains is a simple one: a suspicious package left in public view at a military installation, unnoticed for days, then traced back through a phone call, a vehicle sale and a hurried trip overseas. For prosecutors, that sequence forms the backbone of the case. For the defense, the facts and intent behind it still have to be tested in court.
As of Friday, Ann Mary Zheng remained in custody and Alen Zheng remained overseas, while FBI testing on the device continued. The next milestones are expected to be court proceedings for the sister in federal court in Tampa and any formal move by U.S. authorities to seek the brother’s return.
Author note: Last updated March 27, 2026.