The source also indicated that this case will not be quickly adjudicated.
"In a complex case like this, there will be a lot evidence to collect and it may take a significant amount of time to collect that evidence," he said.
He later added, "In a case like this it will be a very complex trial because of the accusations, and it may take a period of time."
According to military law expert Eugene Fidell, Bales will likely face either life in prison with possibility of parole or the death penalty, a punishment the military hasn't carried out since 1961.
In capital cases deposition testimony is not allowed, Fidell told ABC News. This means if there are Afghan witnesses to the massacre, they must travel to the U.S. to testify in person. And since they cannot be forced to testify some witnesses may decided not to make the trip because they do not trust the U.S. military.
Bales, a father of two, is represented by John Henry Browne a Seattle attorney whose clients have included serial killer Ted Bundy and Colton Harris-Moore, the "Barefoot Bandit." Browne, who said he has taken on only three or four military cases, will have a team that includes at least one military lawyer.
"You couldn't imagine a more difficult case, I don't think," Browne said. "This case has political ramifications, it has legal ramifications, it has social ramifications. So you couldn't really imagine a bigger case."
Bales is being held in an isolated cell at Fort Leavenworth's military prison in Kansas. During a break in his meeting with Bales today, the lawyer told the Associated Press, "What's going on on the ground in Afghanistan, you read about it, I read about it, but it's totally different when you hear about it from somebody who's been there. It's just really emotional."
The sergeant is a man some describe as a virtual case study in what war can do to a person. Neighbors, friends and fellow soldiers all describe him as an easy going family man.
"It's like you're talking about two totally different people," Michelle Cadell, Bales former neighbor, told ABC News. "Every older woman in the neighborhood calls him 'my Bobby,' not Bobby Bales. You don't know who Bobby Bales is. It's my Bobby."
Cadell and her brother, Michael Blevins, grew up across the street from Bales in Ohio and idolized him. Bales played little league baseball and eventually became captain of his high school football team. He was a young man who took care of a disabled neighbor after school and went into finance in his early 20s.
"From the time I was able to walk I was pretty much right at his heels watching what he was doing, being there as much as I could be to learn from him," Blevins said.
Things changed after Bales enlisted in the military following 9/11. Between three tours in Iraq there were scuffles with the law, an assault charge, court ordered anger management and financial troubles.
Karilyn Bales wrote on her blog that her husband was "very disappointed" to not get a promotion last year "after all the sacrifices he has made for his love of country."
The family was planning to move and had just put their house up for sale when the massacre happened.
"They're very supportive, very loving. It's a great family and I'm really happy to be helping them," Browne said.
The Associated Press contributed to this report.