The allegations stem from a large sum of money he sent to a French jihadist in Iraq.
The money "was never intended to go to the Islamic State armed group," insist Vinay's lawyers, Emmanuel Daoud and Laure Heinich.
The sum in question was 10,000 euros. Vinay admits he sent the money to an intermediary in Iraq to help extract his client, a French jihadist named Maximilien Thibaut, at present in Baghdad.
A criminal lawyer, specialised in the defence of jihadists, Vinay was chosen in June 2017 to represent Thibaut, the husband of Melina Boughedir, a 27-year-old French woman sentenced last June in Baghdad to life in prison for joining the Islamic State armed group.
Thibaut "had repented," Vinay's lawyers told AFP. "He wanted to give himself up to the Iraqi authorities to be judged in France or in Iraq," they said.
Vinay maintains he had tried to inform Paris' anti-terrorism unit and relevant authorities in France and Iraq about Thibaut's intentions to hand himself in, but his letters remained unanswered.
Crossed the line
In the end, the criminal lawyer sent the money collected from Thibaut's entourage to Germany, to a contact of his go-between in Iraq, who was meant to organise the jihadist's surrender.
According to other sources quoted by the Journal du dimanche newspaper, the amount transferred by Vinay was a fraction of the overall sum, which would have been as much as 37,000 euros to extract Thibaut and his family and organise their surrender.
But "the man was not saved, he died in the besieged city" of Mosul, according to Vinay's lawyers.
In early July 2017, the old city was the last refuge of many jihadist fighters accompanied by their families, including foreigners.
Yet for French authorities, Bruno Vinay had crossed the line. On 17 January, he was formally put under investigation for "funding terrorism" and "transferring a non-authorised sum superior to 10,000 euros."
In a tweet on Friday, Vinay's lawyers strongly rejected the allegations against their client, who for his part says they are no more than "pure fiction".
The case against Vinay comes at a delicate time for France as it debates how to repatriate Islamic State fighters and their families from Syria, prompted by the withdrawal of US troops.