Director Peter Berg went to great lengths to recreate the moment the bombs went off only to realise his efforts were leaving his extras traumatised.

Actress Michelle Monaghan, who stars in the film alongside Boston native Mark Wahlberg, tells LatinoReview, "They rebuilt the finish line, that set, and it was shot over about three days there. It was incredible. I think there were about 800 extras there.

"Pete and Mark were incredibly forthcoming and candid and very sensitive with the crowd and made sure that they knew what we were doing and how we were doing it, and they made sure that everyone felt safe obviously, not only physically, but also emotionally.

"Everybody felt supported if it triggered any emotions or anything like that (and) there was a tremendous amount of help and support teams standing by. That being said, it was incredible.

"My character was at the finish line, and so therefore I had the opportunity to meet a lot of people that were there (that day) as well. They were people who experienced it first hand, on the actual day that it happened and in turn, decided to come back and be a part of it once again. I found that incredibly humbling... People were so united then and still to this day they still are."

Two 'pressure cooker' bombs exploded at the finish line on 15 April, 2013, killing three and injuring over 260 people.

Terrorist brothers Dzhokhar and Tamerlan Tsarnaev were responsible for planting the bombs.