Weapons expert Dr David Kelly reportedly told of "many dark actors playing games" in an email to a journalist hours before his suicide.
The words appeared to refer to officials at the Ministry of Defence and UK intelligence agencies with whom he had sparred over interpretations of weapons reports, according to the New York Times.
The message gave no indication that he was depressed and said he was waiting "until the end of the week" before judging how his appearance before the House of Commons Foreign Affairs Committee had gone.
The newspaper did not name the recipient of the email.
It said another associate had received a "combative" message from Dr Kelly shortly before he left his Oxfordshire home for the last time on Thursday.
The scientist said in the email that he was determined to overcome the scandal surrounding him and was enthusiastic about the possibility of returning to Iraq.
Dr Kelly was grilled by MPs last week over his comments to reporters about the use of intelligence in the run-up to the war in Iraq. He had denied being the main source for a BBC story about claims that a dossier on Iraq had been "sexed up" to boost public support for military action.
Dr Kelly's wife Janice told the New York Times her husband had worked on Thursday morning on a report he said he owed the Foreign Office and had sent some emails to friends.
She said: "After lunch, he went out for a walk to stretch his legs as he usually does."
Mrs Kelly said she had no indication that her husband was contemplating suicide.