TAMPA — Two people are facing charges after an explosive device was found earlier this month outside the visitor’s center at MacDill Air Force Base.

Indictments unsealed Thursday accuse Alen Zheng, 20, of attempting to damage government property and making and possessing an improvised explosive device. He could face up to 40 years in prison, said Gregory W. Kehoe, U.S. Attorney for the Middle District of Florida.

Ann Mary Zheng, 27, is accused of evidence tampering and being an accessory after the fact in Alan Zheng’s case. She could face up to 30 years in prison.

Kehoe said the incident happened March 10.

Anna Zheng entered a plea of not guilty Thursday. Alen Zheng has yet to appear.

A number of law enforcement agencies worked together on the investigation, including Tampa Police Department, Florida Department of Law Enforcement, Pasco Sheriff’s Office, St. Petersburg Police Department and Pinellas County Sheriff’s Office.

The arrests were announced one day after it was announced that Jonathan James Elder, 35, of Palm Harbor, was arrested and charged with making threats against the base. Elder could face up to 10 years in prison, Kehoe said.

MacDill Air Force Base is home to U.S. Central Command, which is leading U.S. operations in Iran.