New York (CNN) -- The father of a man who admitted to a 2009 plot to detonate explosives in New York's subway system, pleaded not guilty Thursday to a series of new charges brought against him.
Afghanistan native Mohammed Zazi was slapped with seven charges related to the incident, including obstruction of justice, witness tampering and visa fraud, according to Clerk Robert Polemeni of the U.S. Eastern District Court of New York.
If convicted, the 54-year-old Colorado man could face a maximum life sentence in prison.
"[This] does not change anything from our perspective," said Zazi's defense attorney, Deborah Colson, said after the additional charges were filed.
Colson asked that "the public withhold judgment until the facts are revealed."
Federal prosecutors say Zazi conspired with others to "alter, destroy, mutilate and conceal ... glasses, masks, liquid chemicals and containers" with the intent "to impair the objects' integrity and availability for use in one or more official proceedings."
His son, Najibullah Zazi, is also a native of Afghanistan and had worked as an airport shuttle driver in Colorado.
Najibullah Zazi was arrested and pleaded guilty to the bomb plot in February.
The younger Zazi admitted his role in the conspiracy, saying, "In spring 2008, I conspired with others to join the Taliban, to fight along with the Taliban against the United States.
"We were recruited to al Qaeda instead," he said.
While at a terrorist training camp in northwest Pakistan's Waziristan region along the Afghan border, Najibullah Zazi "had discussions with al Qaeda about targets including the New York City subway system," he said.
The younger Zazi said he learned how to make explosives at the camp, later pleading guilty to conspiring to use weapons of mass destruction, conspiracy to commit murder in a foreign country and providing material support to a terrorist organization.
Since Najibullah Zazi's arrest, two of his acquaintances have been indicted in the case, as well as Zazi's father and uncle.
Mohammed Zazi's next court appearance is scheduled for May 12, Polemeni said.