In terms of court structure, there are three levels of criminal trial courts in France, police court, which handles misdemeanors in a local area (with a single judge), correctional court similar to U.S. courts of general jurisdiction which handled most felonies in a local area (with three or one judges and no jury), and the Assize court, for which this is just one in each territory comparable in administrative importance to a U.S. state (a French Department), that handles only serious felonies. The Assize for Terrorism would be a division of the court that handles only the most serious felonies that is reserved for the most serious and politically sensitive of the serious felony cases. While appeals from lower criminal trial courts go to an intermediate court of appeal, appeals from the Assize for Terrorism go to an appellate court panel drawn from the same pool of elite criminal court trial judges (in each case without jurors), and from there, appeals are to the French Supreme Court called the Court de Cassation (which like U.S. appellate courts considers only questions of law and not factual disputes) in Paris with 120 judges broken up into five civil case divisions (called chambers) and one criminal division (also called a chamber) who hear cases in panels of seven to fifteen judges per case. Civil appeals to the Court de Cassation are discretionary like a U.S. state supreme court or the U.S. Supreme Court, while criminal appeals to the Court de Cassation are appeals of right.
In all there are far more judges in the French system. An Assize for Terrorism trial would have 1 examining judge, seven first instance trial court judges, nine second instance appellate judges (with all seventeen of these judges chosen from the elite Court of Assize trial court judge's pool somewhat comparable to federal trial court judges in the U.S. v. state trial court judges in the U.S.), and another fifteen final appeal judges, for a total of 32 judges in the case from start to finish, compared to a typical one trial court judge and twelve lay jurors, three appellate court judges and nine supreme court judges (for a total of 13 judges from start to finish plus 12 lay jurors) in a comparable federal criminal terrorist trial in the U.S. Jurors in the Assize courts for other serious cases in France are also not just randomly chosen citizens, they are a blue ribbon panel upstanding citizens chosen based on merit, like the sort of people who might serve on a zoning board or important committee in a U.S. government. There are no representatives of the working class in a French courtroom.
A typical court in France comparable to the Assize for Terrorism for other serious crimes would have three judges and six jurors, instead of seven judges without jurors (actually nine is only for appellate proceedings from the Assize for Terrorism and is in contrast for three judge appellate panels without jurors in appeals of other serious crimes), and would have less courtroom security measures, but would be similar in broad outline and process. In a terrorism case, the law enforcement testimony and involvement would be more from anti-terrorism agencies and paramilitary gendarmes rather than from ordinary municipal police to the same degree and would often include a significant chunk of testimony by non-French speakers that was translated. A terrorism court would also probably have closed sessions at which confidential state secret evidence not made available to the general public, such as the identity of confidential undercover agents was revealed. An account of this court in French can be found here. Images of the court can be found here, such as this one:
From start to finish, the court process in a French terrorism trial might last four to seven years, with proportionately more presentation of evidence starting earlier in the process and less consideration of legal issues alone. But, unlike a U.S. case resulting in a life sentence or death penalty imposition (something that no longer exists in France), there wouldn't be years of collateral attacks on the conviction as there is in the U.S. system when a very long sentence or death penalty sentence is handed down, and there isn't a split between a state and federal court system.
Also, while French prisons are no picnic, they aren't quite the hell on earth, Lord of the Flies environments seen in U.S. prisons, and have far fewer people serving life sentences or sentences for so many years that they are virtually life sentences. You are more likely to get out of prison alive and comparatively unscathed in France than in the U.S. Sentences for serious crimes in France are shorter and the threshold of offense seriousness at which you are incarcerated for a long period of time is higher in France.
Both have what is known as an inquisitorial system. The key points are summarized as follows by Wikipedia (but this doesn't really give enough of the flavor of it for a fictional account):
Despite high media attention and frequent TV portrayals, examining
judges are actually active in only a small minority of cases. In 2005,
there were 1.1 million criminal rulings in France, while only 33,000
new cases were investigated by judges.7 The vast majority of cases
are therefore investigated directly by law enforcement agencies
(police, gendarmerie) under the supervision of the Office of Public
Examining judges are used for serious crimes, e.g., murder and rape,
and for crimes involving complexity, such as embezzlement, misuse of
public funds, and corruption. The case may be brought before the
examining judge either by the public prosecutor (procureur) or, more
rarely, by the victim (who may compel an instruction even if the
public prosecutor rules the charges to be insufficient).
The judge questions witnesses, interrogates suspects, and orders
searches for other investigations. Their role is not to prosecute the
accused, but to gather facts, and as such their duty is to look for
any and all evidence (à charge et à décharge), incriminating or
exculpatory. Both the prosecution and the defense may request the
judge to act and may appeal the judge's decisions before an appellate
court. The scope of the inquiry is limited by the mandate given by the
prosecutor's office: the examining judge cannot open a criminal
investigation sua sponte.
In the past the examining judge could order committal of the accused,
this power being subject to appeal. However, this is no longer the
case, and other judges have to approve a committal order.
If the examining judge decides there is a valid case against a
suspect, the accused is sent for adversarial trial by jury. The
examining judge does not sit on the trial court which tries the case
and is in fact prohibited from sitting for future cases involving the
same defendant. The case is tried before the court in a manner similar
to that of adversarial courts: the prosecution (and on occasion a
plaintiff) seeks the conviction of accused criminals, the defense
attempts to rebut the prosecution claims, and the judge and jury draw
their conclusions from the evidence presented at trial.
As a result of judicial investigation and defendants being able to
have judicial proceedings dismissed on procedural grounds during the
examining phase, cases where the evidence is weak tend not to reach
the trial stage. Conversely, the guilty plea and plea bargaining were
until recently unknown to French law, and now it only applies to
crimes for which the prosecution seeks a sentence not exceeding one
year imprisonment. Therefore, most cases go to trial, including cases
where the prosecution is almost sure to gain a conviction, whereas, in
countries such as the United States, these would be settled by plea
Appeals would be as to both issues of fact and issues of law, essentially conducting a new trial rehashing all of the issues that are disputed on appeal. And, in France, both convictions and acquittals can be appealed, not just convictions. In a serious case like the kind handled by the Assize courts, if there were any serious question of guilt (and surprisingly often, in terrorism cases there isn't as the accused terrorists often proudly trumpet their acts instead of trying to deny them), there will be two successive events like look like U.S. trials followed by an appeal before fifteen judges in the highest criminal court in the land, all of which was preceded by an examining judge's investigation, where the odds of an acquittal if there is going to be one, is much greater.
On a day to day basis one of the biggest differences between a French criminal trial and an American one is that an American trial is a single, continuous, non-stop event continuing four or five days a week until it is completed, while a French criminal trial in a case such as this one might be intermittent, with the court convening for a few days to hear one group of witnesses, then adjourning for a few days, then hearing another group of witnesses and statements from counsel, and so on. This is particularly true of the examining judge phase of the process.
Also, unlike U.S. criminal cases, the victim with his or her own lawyer, is a party, in addition to the prosecutor representing the state's interest, and the defense counsel representing the defendant's interests.
Basically, French and American criminal trials start the same way, with law enforcement officials and prosecutors marshaling a case against a defendant, and end the same way, with a reasonably similar adversarial trial at which many triers of fact review a compact summary of the results of the investigation.
But, while American trials go straight from the beginning phase to the trial phase (and have much more finality since facts can't be reviewed on appeal and acquittals can't be appealed at all in the U.S.), French criminal trials have an intermediate examining judge phase in which the examining judge pro-actively sifts through the evidence looking (in principle) for the truth, rather than trying to convict or acquit, possibly considering witnesses, testimony and evidence that the conviction minded prosecution and law enforcement community didn't look for, and questions that they didn't ask. Temporally and in their pro-active investigative role, an examining judge's work is a bit like an American grand jury proceeding, but conducted by a single judge interacting with counsel for all sides, rather than a couple dozen ordinary citizens supervised by a prosecutor that has no contact with defense counsel or the victim.
Another distinctive feature of French court procedure v. American court procedure, is that French courts do not keep a verbatim record of the proceedings, just the judges' notes of what they saw. So, there is no court reporter, for example, in a French trial. If there is a question over the fact finding in the original trial the evidence is reviewed in a new trial at the appellate level, rather than by reviewing the record from the previous trial.
A little comment about the judges is also in order.
In the U.S., you become a judge by starting as a lawyer (often as a prosecutor or public defender) which required you to finish both an undergraduate degree and a three year law degree, after which you were successful as a lawyer for many years, and then being appointed as a judge in an at least partially political process as a second career.
In France, you go straight from law school (an undergraduate degree from which many graduates go into business or the judiciary or notary commissions or junior posts in the Council of State the policy/public law branch of the court system, rather than becoming trial lawyers) to the lowest level of trial court judging in misdemeanor court and, if you do a good job, work your way up to lesser felony court trial judge and then to Assize Court trial judge and then from there, if you are very senior and very respected, to the Court of Cassation, in an orderly civil service career path, none of which involves cases against the government and none of which involves constitutional issues. Those people who do go from law school to becoming practicing lawyers in France are less numerous, per capita or per number of judges out there, than in the U.S., and are a more elite bunch of trial oriented lawyers closer to British barristers than U.S. lawyers.
Judges in France are far more risk averse bureaucratically minded people with far fewer political connections than comparable judges in the U.S. and very rarely are in total control of a courtroom handling any matter of consequence. French judges also have less formal control of their courtrooms than U.S. judges do because they don't have contempt of court powers to summarily incarcerate people for misbehaving in the courtroom the way that U.S. judges do. In character and career path, a French Assize judge is a bit like a GS-15 senior member of middle management in a U.S. federal government agency (like a department head or regional manager in the FBI or IRS perhaps), accomplished and important, but neither as partisan nor as personally impressive or egotistical as a U.S. federal district court judge. Even a French Court of Cassation judge in France is more like a federal circuit court of appeals judge in the U.S. in terms of fame and power, a significant judge by all accounts, but not on a par with a U.S. Supreme Court Justice who is known by name by every lawyer in the country and lots of people who aren't lawyers who figures decisively in the national balance of power. Lower court judges in France are much younger than their U.S. counterparts and similar in age to or younger than U.S. judicial law clerks, and are much more numerous (although their system is very top heavy compared to the U.S.), while Assize judges in France are fairly comparable to U.S. general jurisdiction trial court judges in age, but have far more experience as judges, although they've never been attorneys representing clients, and far less political clout. The household names in the French legal world are Constitutional Court members, the leading members of the Council of State, and the leading law professors (who moonlight as lawyers as well) whose treatises substitute for the bulk of the appellate case law that U.S. law students study, not the judges of the highest ordinary appellate courts.
To somewhat overstate the matter, U.S. judges are historically successors to feudal aristocrats holding court, while French judges are historically successors to really senior and well educated court clerks.
Emmanuel Carrère wrote "The Adversary: A True Story of Monstrous Deception" (2001), is a best selling non-fiction account of a 1993 murder trial in France. And, an account like this one would have far more detail useful to an author that pretty much all of the leading academic literature on the topic which is too dated and too non-specific to be of much use.
Italian and French criminal procedure are quite similar, so another good source of material, which received lots of media coverage, would be the criminal trial of American Amanda Knox for murder.