A federal grand jury investigation has so far spent two weeks examining the September 16 firefight.
People close to the case told AP that authorities have focused the number who could face charges to about three of the dozen or more guards on the security detail.
A decision may still be months away.
The people who discussed the case noted concerns about testimony given by the four Blackwater guards who have so far appeared in front of the secret panel.
Details were discussed on condition of anonymity because of the sensitive nature of the information.
The concerns stem, in part at least, from the fact that one defence lawyer and law firm represent as many as 10 guards, raising worries that their stories could be co-ordinated.
Official retires
In a separate development, a top US state department official who was quizzed over his brother's links to Blackwater, has announced he is stepping down.
Inspector general Howard Krongard announced he would retire on January 15, in a letter to George Bush, the US president.
Congressman Henry Waxman, who chairs an oversight committee that monitors private contractors operating in Iraq, has accused Krongard of blocking investigations into contracting fraud and arms smuggling there.
In a dramatic hearing last month before a house oversight panel, Krongard first insisted under oath that his brother, Alvin, had no affiliation with Blackwater,
Advisory role
Krongard then called his brother during a break and discovered that in fact he was an adviser to the company.
He returned to the hearing room and announced that he had been wrong.
His brother resigned from his Blackwater position two days after the hearing.
Gonzo Gallegos, a state department spokesman who announced the inspector general's decision to retire, said: "We thank him for his dedication to public service and wish him well in the future."