Washington (CNN) -- In the wake of the leak of thousands of classified documents, the U.S. Army has expanded its criminal investigation into a soldier allegedly involved in the earlier leak of a combat video and thousands of military documents, according to the Pentagon.
The expanded investigation was confirmed by Col. David Lapan at the Pentagon.
According to a U.S. military official who asked not to be named because he was not authorized to talk about the investigation, the probe by the Army's Criminal Investigation Division into Pfc. Bradley E. Manning was expanded to look at potential accomplices and what military or U.S. government systems the information came from.
CNN was unable to reach Manning's attorney.
The leak of documents published by the website WikiLeaks.org is a "very big breach," Pentagon spokesman Geoff Morrell said on Monday.
"Look, there's a slew of people who have access. It will be, as all these investigations are, very difficult, but we are determined to find out who is responsible for this and to make sure they pay or are held accountable for it," Morrell said in an interview with CNN's John King. "This is a very big breach for which there must be consequences."
The investigation was expanded because investigators believe Manning has a connection to a number, but not all, of documents released on WikiLeaks.org on Sunday. The Army is also working with other U.S. agencies in the investigation, according to Army CID spokesman Christopher Grey.
Manning, 22, of Potomac, Maryland, was charged with eight violations of the U.S. Criminal Code for allegedly illegally transferring classified data, including an earlier video that wound up on WikiLeaks. He has been accused of "wrongfully introducing a classified video of a military operation filmed at or near Baghdad, Iraq" around July 12, 2007, "onto his personal computer, a non-secure information system."
Manning had top-secret clearance as an intelligence analyst with the Army while he was stationed in Iraq. He was detained in June and sent to the U.S. base in Kuwait for his connection to the release of the classified U.S. military combat video showing the shooting death of Iraqi civilians and two journalists in 2007 by a helicopter gunship.
The Army is trying to trace who Manning's contacts were and on what computer servers he had to possibly access a plethora of information from U.S. military documents to Department of State cables, according to the official.
Manning has not been cooperating with Army investigators; the official said Manning has invoked the Fifth Amendment and is refusing to answer questions from investigators.
Manning is still being held by the U.S. military in Kuwait while his unit begins to rotate back to the United States.
Vice President Joe Biden and his wife will greet part of Manning's unit, the 2nd Brigade of the 10th Mountain Division, as it returns to Fort Drum, New York, on Wednesday.
Manning could be additionally charged as the Army's investigation continues, according to the official. At the moment, he has been charged with illegally transferring classified data onto his personal computer and adding unauthorized software to a classified computer system in connection to the leaking of the helicopter video.
He has also been charged with communicating, transmitting and delivering national defense information to an unauthorized source and disclosing classified information concerning the national defense with reason to believe that the information could cause injury to the United States in connection to the leak of the same video.