WHAT could have possibly possessed a young medical student in the US to walk into a busy movie theatre and kill 12 innocent people?
It's a mystery detectives investigating the worst massacre since the 2007 Virginia Tech killings have been under immense pressure to solve but two days after a masked gunman opened fire on theatre goers at a country-town premier The Dark Knight Rises, the motive is still unclear.
All police do know is that on Friday evening (Eastern Standards Time) a masked man walked into the Century 16 movie theatre in Aurora, Colorado, stood in front of the crowd, released poisonous gas and shot people at random.
Police will allege that man was 24-year-old James Holmes, who was arrested near a car soon after the attack.
On the weekend, bomb technicians were called in to help detectives search Holmes's apartment.
Inside, they allegedly found a network of explosives and trip wires.
Mr Holmes's mother reportedly told US journalists she had "sensed" her son was the killer when she saw reports of the shootings on the news.
The French premiere of the movie was cancelled on the weekend out of respect.
A baby was among the 58 people injured during the Colorado attack.
12 people have been confirmed dead, the youngest, a six year old girl.
In a radio address on Saturday morning, US President Barrack Obama urged Americans to "pray" for the victims and their families.
The mass shooting was the worst to hit Colorado since the 1999 Columbine High School massacre where two students shot and killed 12 class mates and a teacher.