Thirteen people were shot dead by paratroops in Londonderry on 30 January 1972. A 14th person died later.
The Guardian says Lord Saville's report - which has taken 12 years to compile and is due to be published on Tuesday - will say some were unlawfully killed.
The government said such speculation added to the stress of those involved.
A spokesperson for the Northern Ireland Office said: "The report will be published in a few days and everyone can read it then.
"The people directly affected by all of this - the families of those killed and injured, and the soldiers - have waited a long time for this report, and speculation of this kind only adds to the stress and anxiety that they must all feel."