John Lee Malvo's defence team has condemned police for the manner in which the interrogation of the 17-year-old was conducted and for their subsequent leaking of the story to the Washington Post at the weekend.
Citing unnamed officials, the paper had reported that Mr Malvo had admitted to pulling the trigger on several occasions during a shooting spree in the Washington area last month, which left 10 people dead and three wounded.
It is unclear at present how these alleged statements may affect the case of 41-year-old John Allen Muhammad, who has been portrayed as the chief suspect in the case.
The two men were arrested on 24 October after one of the nation's biggest ever manhunts.
'Poisoning the jury'
US Attorney General John Ashcroft released both men from federal custody last week after deciding they should first face trial in Virginia - where both may face the death penalty - rather than Maryland which saw more fatal shootings but which does not execute juveniles.
The two suspects will face separate trials for different murders, but prosecutors said they may rely on evidence from any or all of the attacks around Washington DC, and crimes across the country which have now been linked to the men.
Mr Malvo was questioned by investigators on Thursday - an interrogation which his lawyers say was unconstitutional.
"The police are flooding the media and poisoning the jury poll with their own paraphrasing and subjective interpretations of statements made during an unconstitutional interrogation," said defence attorney Michael Arif.
"If in fact those are the statements Mr Malvo made, there will be a motion to suppress those statements, as certain as the sun rises in the east."
According to the Washington Post, Mr Malvo admitted to pulling the trigger in several of the attacks. The newspaper reported that these included the fatal shooting of FBI analyst Linda Franklin, who was gunned down in suburban Virginia on 14 October.
Authorities have not mentioned Mr Malvo by name, but have already said that a "juvenile" will face capital murder charges for the shooting of Ms Franklin.
On Friday, Mr Muhammad appeared in a Virginia court where he has first been charged with the killing on 9 October of Dean Meyers, 53, who was shot at a petrol station.