Videos of the May 16 2016 assault, which have been viewed hundreds of thousands of times on YouTube, show youths dressed in black, most with their faces covered, surrounding the vehicle in the midst of traffic in the heart of the French capital.
One can be seen kicking in the window on the driver's side, and another hurling a flare into the vehicle, eventually causing it to burst into flames.
The incident took place on the sidelines of a demonstration staged by a police union over anti-police violence during protests over contested labour reforms.
The attackers struck after a counter-demonstration against police brutality.
After the driver, Kevin Philippy, got out of the car, assailants struck him with metal bars.
"Kung Fu Cop"
Philippy, who was nicknamed "Kung Fu Cop" for his technical prowess in barring the blows he received, is a civil plaintiff in the case, along with his female colleague, Allison Barthelemy, and the Alliance police union.
Some of the defendants have admitted their involvement. Three have been in custody since the assault, while five are under house arrest. The man accused of throwing the flare into the car is still on the run.
The attackers, who include students and teaching assistants, initially faced charges of attempted murder of a person holding public office but the charges were reclassified to "aggravated violence against police officers".
One is an American and two of the others on trial are brothers who are descendants of the famous French writer Georges Benarnos.
While some police officers have called for the defendants to be tried for attempted murder, the head of the Alliance union, Jean-Claude Delage, simply asked the court to send a "strong signal" with its verdict.
The trial is scheduled to end on Friday.