Swat Valley, Pakistan (CNN) -- Six men have been arrested in connection with the shooting of Malala Yousufzai, the teenage activist who spoke out against the Taliban, but the main suspect remained at large, Pakistani police said Wednesday.
Police identified Atta Ullah Khan, a 23-year-old man from the Swat district where Malala was attacked, as the primary suspect. Police said they were searching for Khan, who was studying for a master's degree in chemistry.
The Swat Valley in northwestern Pakistan is a Taliban redoubt.
In addition to arresting six men -- all of them from Swat -- police have detained Khan's mother, brother and fiancee. The suspect's relatives were not accused of involvement but are being questioned, a senior police official told CNN.
The official did not say what role Khan may have played.
Khan had studied for a Bachelor of Science degree in physics at Jahanzeb College in Swat.
Alam Zeb, the school's principal, said Khan had given school officials three or four dates of birth. Zeb condemned the attack and said he was surprised to hear that a former student may have been involved.
The 15-year-old girl, who has become a symbol of courage after being shot in the head by the Taliban for demanding education for girls, is being treated at a hospital in Birmingham, England.
On Wednesday, she remained in stable condition and "continues to make good progress," the hospital's website said. She is expected to need "a significant period of rest and recuperation" before undergoing reconstructive surgery, Dr. Dave Rosser, medical director of University Hospitals Birmingham, said last week.
Malala was fighting an infection, but was able to move her extremities and has stood with help from nurses, the hospital said.
Malala's family remains in Pakistan.
Malala can't speak because a tube has been inserted into her trachea to protect her airway, which was swollen after her gunshot injury, but she was writing coherent sentences, Rosser said.
The Pakistani Taliban have claimed responsibility for the October 9 shooting and vowed to kill Malala, if she recovers.
Journalist Saima Mohsin and CNN's Nasir Habib contributed to this report from Swat