@mismi,
I wouldn't shed any tears for the younger brother. He caused as much heartache as his brother did. When he placed his backpack on the ground, he knew full well what the result was soon to be.
Your's is by no means the lone expression of sentiment for the younger brother and it raises the interesting question of why people somehow feel the need to find a sympathetic figure in events like this.
Apparently the appearence of almost childish innocence found in the photos of his face; plastered all over TV, is able to invoke an instinctual response in some people.
I feel quite sure that if we had a running film of his face over the course of this heinous crime we would find images that revealed the sickness inside him that is often referred to as evil.
To the extent anyone can be considered evil, he and his brother fit the bill. They actively planned to kill and maim as many truly innocent people as they could. They walked among their potential victims and saw them enjoying life and family and had no compelling second thoughts about destroying them. In fact, if you examine some of the stills from the video of the brothers you will detect a smirk on the face of the younger brother, as if he was enjoying the thought of the power he had over the people on the street.
Any sympathy for the younger brother is totally misplaced. How much strength is required to not participate in murder and maiming?
I suppose the notion that the dark and twisted older brother somehow bent his younger sibling to his evil will helps people deal with the fact that someone who can look like a choir boy and be considered a "normal, good guy" by people who have known him for years can be a monster.
No doubt his defense team will try and paint exactly the picture you've chosen to see: that of a helpless, hero worshipping boy, turned to the dark side by the swarthier older brother who actually looks like someone who might commit murder. I hope and doubt that a jury of his peers will buy such a ploy.