Colonel Francois Daoust, the institute’s director, said: “Subject to the amount of body parts found, the time period could fluctuate between two months at the least, and four months.
“It is better to work at the rhythm of the science than to rush ahead and thereby run the risk of making mistakes in the identification.”
He added: “We cannot promise that we will be able to identify all of the victims.”
German prosecutors have said Andreas Lubitz, 27, who deliberately caused the crash in the French Alps, had therapy for suicidal tendencies some time before getting his pilot’s licence.
And he was being treated by a psychotherapist, Dusseldorf prosecutor’s office spokesman Christoph Kumpa said.
“At that time he was being treated for what is documented as being suicidal,” Mr Kumpa said.
He added that Lubitz paid several visits to doctors right up until the time of the crash but these did not involve suicidal tendencies.
No suicide note “or anything like that” was found in searches of Lubitz’s German residences, Mr Kumpa said.
There was also nothing in his personal, family or professional background to provide any hints “about his motivation”, he said.
He also said Lubitz was not suffering from any “organic medical illness”.
Cockpit voice recorder evidence has indicated that Lubitz deliberately put the Airbus A320 into a descent after locking out the captain.
All 150 people on board, including three Britons, were killed in the crash last Tuesday.
Mr Kumpa was speaking as the grim search for remains carried on in southern France.
There were reports that Lubitz’s girlfriend was pregnant with his child and that the co-pilot, as well as allegedly having mental health issues, had been receiving treatment for an unspecified vision problem which could have affected his ability to carry on working as a pilot.
Authorities have already revealed that he hid from his employers a sick note declaring him unfit to work on the day of the disaster, and Bild has said he previously told an ex-girlfriend: ‘’One day I will do something that will change the whole system, and then all will know my name and remember it.’’
The Britons killed were Mr Bramley, 28, originally from Hull, Martyn Matthews, 50, from Wolverhampton, and seven-month-old Julian Pracz-Bandres, from Manchester, who died alongside his mother, Marina Bandres Lopez Belio, 37, originally from Spain.