President Obama, and the First Lady are attending an memorial service for the victims of the Boston Marathon at the historic Cathedral of the Holy Cross. The president is trying to comfort Boston residents at the interfaith service titled "Healing Our City." Security was tight outside the 140 year old cathedral which is packed with about 2,000 dignitaries and mourners. The president is also meeting with some of the 170 people who were hurt in the bombings, and first responders who rushed to the scene to help them. Hundreds of mourners lined up early outside of the cathedral of the holy cross. People started arriving overnight hoping to get a seat inside. Sources tell CBS News investigators may release a photo of a man seen placing a bag at the site of the second bombing. Security cameras at a Lord & Taylor store captured the man moments before the explosion. He is described as a young white man who was carrying a backpack and talking on a cell phone. CBS News senior correspondent, John Miller says Investigators think the man could be the bomber. Their operating theory is the bag that he put down is the bomb. Investigators are also looking at cell phone records from the area, and facial recognition programs hoping to zero in on their man of interest.