In Tampa, Florida, the brother and sister are now facing federal indictments related to an “improvised explosive device” discovered at MacDill Air Force Base last week.

The indictment charges 20-year-old Alen Zheng with attempting to damage or destroy the Visitor’s Center at MacDill through the creation of an improvised explosive device, commonly referred to as an IED.

At a Thursday afternoon press briefing, FBI officials revealed that Alen’s attempt to detonate the device at the Visitor’s Center on March 10 was unsuccessful. Although a 911 call had warned of a bomb on the base, MacDill personnel initially found no evidence of a device.

It wasn’t until Monday, March 16, that the explosive was discovered by base officials.

Federal authorities state that shortly after placing the bomb, Alen and his 27-year-old sister, Ann Mary Zheng, left the country, fleeing to China. Additionally, they reportedly sold the car used to transport the IED from their residence to MacDill.

Records show Alen and Ann Mary Zheng both lived together at a home in Land O’ Lakes.

During the investigation, FBI officials were able to identify the number used in the initial 911 call, which was traced back to Alen, who purchased the phone at Best Buy. 

Authorities say they were able to retrieve footage from Best Buy which helped them identify Alen purchasing the phone at the store, as well as the vehicle that he and his sister sold on CarMax prior to fleeing the country.

FBI officials said Ann Mary Zheng came back to the US on March 17 and was taken into custody, however, Alen is still in China.

On March 18, a search warrant was obtained for the Zheng home, and federal officials say they found “IED components consistent with the bomb that had been placed at MacDill Air Force Base.” FBI agents also reportedly spoke with Ann Mary Zheng and her mother. They both conceded that Alen had told them about the bomb planted at MacDill. 

In addition, federal officials say traces of explosive residue were found in the vehicle the siblings sold.

Alen Zheng is facing attempted damage of government property by fire or explosion, unlawful making of a destructive device and possession of an unregistered destructive device. According to the indictment, if convicted, he faces a minimum penalty of five years, up to 40 years, in federal prison. 

In a separate indictment, Ann Mary Zheng is accused of evidence tampering and being an accessory after the fact in Alen Zheng’s case. 

According to the indictment, Ann Mary Zheng “did corruptly alter, destroy, mutilate and conceal” the vehicle, a 2010 black Mercedes-Benz GLK 350, as part of the case.

If convicted on all counts, officials say she faces a maximum penalty of 30 years in federal prison. 

The suspects’ mother has also been taken into custody on an immigration violation but has not been charged in connection with the bombing attempt.

Federal officials say the motive is unknown, and both siblings are known to be American citizens.

An investigation is ongoing.