Lips are tightly sealed around the three-and-a-half hour movie, but it is based on the best-selling book by US journalist David Grann about a wave of murders among the wealthy Osage Indians in the 1920s and the birth of the FBI.

Cannes has had no shortage of splashy moments since it kicked off on Tuesday with the controversial appearance of Johnny Depp in his first movie since a bitter trial with ex-wife Amber Heard.

He played French king Louis XV in “Jeanne du Barry”, which received middling reviews, and festival director Thierry Fremaux irked online critics by saying “I don’t care” about Depp’s legal woes.

The festival also saw an emotional appearance from Harrison Ford, receiving an honorary Palme d’Or at the world premiere of “Indiana Jones and the Dial of Destiny”.

At the risk of turning this year’s Cannes into a festival of ageing Hollywood males, there was also an honorary Palme for Michael Douglas, and an appearance from Sean Penn as a grizzled New York paramedic in “Black Flies”.

Meanwhile, the main competition for the top prize Palme d’Or is heating up.

Among the early front-runners, is British director Jonathan Glazer’s “The Zone of Interest”, a horrifying look at the private lives of Nazi officers working at the Auschwitz concentration camp.

Also getting plaudits is “Four Daughters”, Kaouther Ben Hania’s clever semi-documentary about a Tunisian mother trying to deal with the radicalisation of her children.

A total of 21 films are competing for the hearts of a jury led by last year’s winner, Ruben Ostlund (“Triangle of Sadness”), ahead of awards night on May 27.

Italian-American icons

But all eyes will be on the red carpet this Saturday as three icons of Italian-American cinema make their way to the Palais des Festivals.

DiCaprio and De Niro are both long-time Scorsese collaborators. But he has never before cast them in the same film, apart from a funny short in 2015, “The Audition”, in which they competed for a part in his next movie.

The film world is also painfully aware that it may be one of the last movies from the master behind “Goodfellas”, “Raging Bull” and “Taxi Driver”.

In a poignant interview earlier this week, the 80-year-old Scorsese told Deadline: “I’m old… I want to tell stories, and there’s no more time.”

“Taxi Driver” won the Palme d’Or in 1976, but he has not been back in the Cannes competition since 1985’s lesser-known “After Hours”, though he did serve as jury president in 1998.

“Killers of the Flower Moon”, which was funded by Apple, is showing out of competition.