A survey of 4675 US adults conducted after the 15 April attacks and the manhunt that was launched for one suspect, Tamerlan Tsarnaev, left a deep impact on viewers.
Even though many of the gory images were cropped and modified by many media companies, there were still many unedited pictures doing the rounds which were captured by witnesses that were available on social media.
Even those that were not directly connected with the incident were affected emotionally.
"Media exposure was a stronger predictor of acute stress response than having been there," experts said.
"It wasn't that the direct exposure was not important, it was just that above and beyond having been there, media exposure was an even stronger predictor of acute stress response. It doesn't become PTSD until the characteristic problems go on for more than six weeks and interfere in some significant way with people's lives. People should be aware there is no psychological benefit to repeated exposure to pictures of horror."