Archbishop Dominique Lebrun of Rouen announced the opening of inquiry at the end of the chrism Mass April 13.

Father Hamel was killed July 26, 2016 as he celebrated Mass at Saint-Etienne-du-Rouvray Church near Rouen when, police said, two young men who claimed allegiance to the Islamic State stormed the church. After taking several hostages, the attackers slit Father Hamel's throat and seriously injured another parishioner. Following a standoff, police killed the attackers, ending the hostage situation.

Traditionally, the Vatican requires a five-year waiting period after the death of a candidate for sainthood before a cause is opened. Pope Francis waived the rule in response to pleas from French Catholics last fall.

The inquiry is the first step toward beatification and possible sainthood.

The Pope called Father Hamel a martyr during a special requiem for the priest Sept. 14 in the chapel of Domus Sanctae Marthae at the Vatican.

"Father Jacques Hamel had his throat slit on the cross, at the exact moment he was celebrating the sacrifice of Christ's cross. A good man, meek, brotherly and who always sought to make peace, was murdered as if he were a criminal. This is the satanic line of persecution," the Pope said.

The inquiry is expected to take several years even though the beatification of a martyr is a simpler process because there is no need to prove a miracle occurred through his intercession.

An archdiocesan statement said about 50 people will be contacted. The group will include witnesses at the Mass as well as family members, fellow priests and others who knew Father Hamel.