The note provides a fairly detailed account of the suspect's evolution towards a more radical form of Islam since 2009, pointing out that police had remarked he had "suspicious behaviour".
Homeless and unemployed, Alexandre D applied for jobs in Rambouillet where he "demanded not to work with women".
He also came under scrutiny after a street prayer in 2007 while authorities had his DNA profile on record after a series of petty crimes as a minor.
Detectives identified him through video footage, in which he can be seen praying near the crime scene eight minutes before the attack, as well as buying two knives an hour before. DNA was also found on items left at the scene in a plastic bag, including a knife and a fruit juice bottle.
Francois Molins, the Paris prosecutor, said the suspect "owned up to the attack" shortly after his arrest and added that he "acted in the name of his religious ideology".
The prosecutor denounced the suspect's "quite clear intention to kill" Cedric Cordiez, 23, who was attacked from behind.