French news website Médiapart's said that their six-month investigation led to the discovery that the intelligence agents became aware of threatening online messages by one of Fr Jacques Hamel's killers earlier than was claimed.
While it had been reported the local intelligence officers received the information on the day of the attack in July 2016, the publication said they became aware five days prior but failed to pass it on to the national French intelligence.
It is alleged the police intelligence unit doctored the files in a bid to make it look as if the original report was only written on the day of the attack itself.
The claims have placed counter-terrorism agencies under further scrutiny over a series of terror attacks that have left 239 people dead in France since 2015.
On 26th July 26 2016, Adel Kermiche, and Abdel-Malik Petitjean, who were both 19 and Islamists, burst into a church in the small town of Saint-Etienne-du-Rouvray in Normandy and slit the throat of the 85-year-old priest.
The priest shouted "Satan, get out of here, get out, Satan" during the attack.
The killers were shot dead by police who stormed the church some 45 minutes after they took a number of people hostage.
A process to decide whether the murdered priest should be made a saint has been officially opened.
Canonisation candidates must usually have been dead for at least five years before a Cause can start, however, Pope Francis ruled in October 2016 that an exception should be made for Fr Hamel.