>> martha: breaking tonight, the horrific images coming out of manchester, england, provide a chilling reminder of similar attacks on some of the youngest and most vulnerable in our society in years past. for more on the history of what we have seen, we go to trace gallagher in our west coast newsroom. >> the department of homeland security issued a warning to americans last september that isis was turning his attention away from military targets and venues with large numbers of civilians. it was already horrifyingly apparent, just three months before that morning, 29-year-old omar mccain open fire and tied back inside the pulse nightclub in orlando, killing 49 and wounding 53 others. he claimed to be an islamic soldier who had pledged his allegiance to isis. and just six months before the orlando attack, isis affiliated terrorists hit numerous targets in paris, including the