This week, police officers and firefighters who risked their lives can see private screenings of the new Oliver Stone film about the collapse of the twin towers and the ensuing human tragedy.

Although the director's gesture cannot be taken as other than a tribute to their sacrifice, many police unions have already launched a warning that the experience (or the revival of it) may result to be too traumatic.

The 'World Trade Center' movie stars Nicholas Cage as one of the two Port Authority of New York and New Jersey police officers who remained under the rubble caused by the collapse of the towers and where found and rescued 22 hours later. The film opens in the United States on August 9.

The co-producer, Michael Shamberg, explained the reason behind the special free screenings as follows: 'Emotionally, it's important that these men and women have the opportunity to see the film first, though only if they feel comfortable'.

All the police unions sent a warning to their officers according to which, should they consider attending to the screening, they must be aware that the experience may cause post-traumatic disorder, whose symptoms range from depression to mood swings and panic attacks.