Nice attack: 'Any radicalisation of Nice attacker must have been quick,' French Interior Minister saysReuters

In the days before the horrific attack, relatives said that Bouhlel asked friends to hide the money and take it to his family in Msaken, Tunisia. Where the cash came from is a mystery as Bouhlel has been unemployed for several months, leading to suspicions it could have come from an Islamic terrorist group.

The 31-year-old French-Tunisian driver's brother said he received the sum of £84,000 in cash. Jaber, his brother, revealed he had not seen his brother for many years and the money was unexpected.

"Mohamed sent the family 240,000 Tunisian Dinars (£84,000) in the last few days," Bouhlel's brother told MailOnline. "He used to send us small sums of money regularly like most Tunisians working abroad. But then he sent us all that money, it was fortune.

"He sent the money illegally. He gave cash to people he knew who were returning to our village and asked them to give it to the family."

Bernard Cazeneuve, the French interior minister said the killer "appears to have become radicalised very quickly". while a neighbour of his ex-wife added: "Mohamed only started visiting a mosque in April."

The Bastille Day attack was claimed by Isis and investigators say they have found proof that Bouhlel was in contact with known Islamic radicals by checking his phone records.

But an intelligence source told the Telegraph: "That could just be a coincidence, given the neighbourhood where he lived. Everyone knows everyone there. He seems to have known people who knew Omar Diaby (a local Islamist reportedly linked with the Al Nusra group close to Al Qaeda)."

Bouhlel's father also denied claims that his son was an Islamic State militant, stating the killer had "nothing to do with religion" but was suffering from mental illness. Mohamed Mondher Lahouaiej-Bouhlel told French media from his Tunisian home: "He had some difficult periods. I had to take him to a psychiatrist who gave him medicine. He had a very serious illness."

He added: "What I do know, is that he never prayed, he never went to mosque, he had nothing to do with religion... He was alone, depressed, always alone."

Mohamed Lahouaiej Bouhlel drove a lorry into crowds, killing 84 during Bastille Day celebrations on 14 July, before he was shot dead by police.