Marc Lépine and Clifford Robert Olson Jr

Marc Lépine (mass murder):
Since his teen years, he had been sullen and angry –Canadian. His mother had divorced his father over the issue of abuse, and Marc Lépine always got beaten by his father.
The boy so hated him that when he was 13, he changed his name to Marc Lépine.
Nevertheless Lépine adopted his father's views about women as servile and second-class. They were not men's equals.In his mind, women had a specific place in society and they should stay there.
As he grew older, he believed that independent women were pushing him out of his own rightful opportunities. Someone, he believed, had to teach them a lesson and he decided that it would be him.
Marc Lépine (on December 6, 1989) "You're all a of bunch of feminists! And I hate feminists!"

Monique Lépine (Marc Lépine’s mother): "He was a brutal man, who did not seem to have any control over his emotions... It was always a physical gesture, a violent gesture, and always right in the face."
On December 6, 1989, Marc Lépine went into the École Polytechnique at the University of Montreal, located on the north slope of Mont Royal. It was the largest engineering school in Canada, with about 5,000 students enrolled at that time. He ran through the whole school, shooting a rifle at women and people who where in his way. In the end, he turned the rifle's barrel toward his own face, pressed the muzzle against his forehead, and pulled the trigger.
All in all he had killed 14 women and wounded 13 other students of both genders.
It took a while to piece together why he had caused so much slaughter, but soon came out that he was an anti-feminist. He had wanted to shoot only women.

Clifford Robert Olson Jr (serial killer):
Clifford Robert Olson Jr born on January 1st, 1940 in Vancouver, B.C., is a canadian serial killer.In his teenage years, he did crimes like B&E's, robberies, theft, etc.
In 1974 he sexually attacked a 17-year-old fellow inmate. After being released he indecently assaulted a 7-year-old girl in Nova Scotia. This was the beginning of his sexually deviant and murderous criminal activities.
Olson had killed 10 children in southern British Columbia and, by the time he was finished, 11 would be dead. When he was arrested, only three bodies had been discovered and identified. The police did not yet know how many children had been murdered.
Olson said he wanted to be hired at a salary of $3,000 a month. In exchange, he claimed he would provide information about the disappearances.

Mass murders are the act of murdering a large number of people at the same time while serial killers are person who murder three or more people over a long period of time.
One big difference between serial killers and mass murderer is,that mass murders think that they have to accomplish a mission, and have to do it, while serial killers enjoy (sexual) assaulting,killing etc. people.
Marc Lépine did not feel pleasure by killing all these women but, Clifford Olson certainly did.

I do not think that we could ever stop people like this,because sometimes you do not even know that people are mentally oder emotionally disturbed and need help.
When you find out that somebody is a serial/mass murderer it's mostly already too late.
Another problem is that serial killers are mostly very smart people,and so it is hard too catch them.
But I also think that it is possible to stop some of those killers, if you keep your eyes open and
immediately call the police if you see people who announce murders. (e.g. videos via internet)