Mumtaz Qadri, 26, became a hero to many Pakistanis on 4 January when he killed Punjab Governor Salman Taseer - the man for whom he worked as a bodyguard.
Mr Qadri says he was angered by the governor's backing for proposed amendments to the country's blasphemy laws.
Police officials say he had made up his mind to kill someone five days earlier, when he heard an inflammatory speech by a cleric at a religious gathering in Rawalpindi.
Governor Taseer just became his easiest target.
But psychologists say the story must have started earlier.
Some years ago, Mr Qadri, who had just finished high school and trained as an elite police commando, was assigned to the security detail of a United Nations mission.
On one occasion, members of the mission needed to stop a cab, but the cab they hailed to did not stop.
Mr Qadri became angry and started firing his official gun.
Luckily, no one was hurt. But the incident established Mr Qadri as what the police official who described the episode called a "trigger-happy" individual.
"These types of people hold their emotions or faith as the highest value, and they never repent," says Dr Zahid Mehmood, who heads the Department of Clinical Psychology at Government College, Lahore.
A police video of Mr Qadri's interrogation shows him insisting: "Yes, Salman Taseer got what he deserved for insulting the Prophet."
Mr Qadri's brother, Dilpazeer Awan, describes him as a "gentle, warm and obedient" person who prayed five times a day, as Muslims are obliged to do.
"He was younger than all his brothers, but he was far more religious than us," Mr Awan told the BBC.
But police officers investigating the case think otherwise.
"It is wrong to say that he was deeply religious," says Bin Yameen, the head of police operations in Islamabad.
"His profile shows him to be a worldly person, someone who would grow a beard, then shave it off and grow long hair. And he often fell in love with different women.
"If he were such a lover of the Prophet, he would have committed a murder a long time ago - as he has often been on security details assigned to take offenders booked under the blasphemy law from jail to the court and back."
Mr Yameen confirmed that Mr Qadri, along with 11 other elite police guards, had been declared a "security risk".
"We have asked the responsible officials to explain their position, as Mumtaz Qadri should not have been assigned to Governor Taseer's security," he said.
Many police officials believe psychological profiling may help in such matters, although it is not foolproof.
"Psychological profiling is essential to determine the mindset of operatives who are assigned to sensitive duties," says the head of the National Police Academy, Chaudhry Yaqoob.