The Taliban have claimed responsibility for the shooting, saying that the girl was promoting "Western thinking."
Providing more details, a Taliban spokesman said the top leadership of the Taliban's Swat Valley chapter decided two months ago to kill Yousufzai in a carefully planned attack after her family ignored repeated warnings.
Police have been questioning people in the town of Mingora, where the shooting took place.
Mingora police chief Afzal Khan Afridi said arrests had been made, but he declined to give any details about the number of people detained or what role they're suspected in having in the shooting. He said he did not want to endanger the ongoing investigation.
The Taliban spokesman, Sirajuddin Ahmad, said her family had been warned three times — the most recent warning coming last week — before the decision was made to execute her.
Ahmad said the local Taliban leader Maulana Fazlullah and his deputies selected three attackers, including two trained snipers, who carefully studied the girl's route home from school.
Even before the Taliban took over the Swat Valley, Fazlullah's radio broadcasts spread fear among residents in the area. The group first started to exert its influence in 2007 and quickly extended its reach to much of the valley by the next year. They set about imposing their will on residents by forcing men to grow beards, preventing women from going to the market and blowing up many schools — the majority for girls.
Malala wrote about these practices in a journal for the BBC under a pseudonym when she was just 11. After the Taliban were pushed out of the valley in 2009 by the Pakistani military, she became even more outspoken in advocating for girls' education. She appeared frequently in the media and was given one of the country's highest honors for civilians for her bravery.
Fazlullah, along with much of the Swat Taliban's top leadership, escaped the offensive and is believed to be operating from a base in eastern Afghanistan and sending fighters back across the border to attack northwest Pakistan.
Yousufzai is now being treated at a military hospital in the city of Rawalpindi. A military spokesman says her condition is satisfactory but the next 36-48 hours would be crucial.