ISLAMABAD: Nadir Soofi, a gunman shot dead after opening fire at a Texas exhibit of caricatures of the Prophet Muhammad (PBUH), was a popular schoolboy in Pakistan but struggled to adjust to the United States after moving there as a teen, friends said on Tuesday.

Police say disappointment, alienation, and a search for belonging inspired Soofi and his roommate, Elton Simpson, to attack the exhibit and contest to draw Prophet Muhammad (PBUH) cartoons on Sunday.

Such depictions are offensive to Muslims and often spark violence. Event organisers said the event was defending free speech.

The two gunmen were shot dead by a police officer before they could kill anyone.

Read more: Texas police shoot dead two gunmen at Prophet (PBUH) caricature exhibit

Friends in Pakistan, who studied with Soofi at the elite International School of Islamabad, were stunned to discover that police had identified him as was one of the attackers.

“When he was in Islamabad, he had a great life. His mom was an American who taught art at the school, he was in plays, popular with girls,” said one of Soofi's best friends at school.

“His nickname was Goofy” because of his sense of humour, said the man, who declined to be identified to preserve his privacy.

Another classmate said Soofi played the lead in the school's production of the play “Bye Bye Birdie”.

“He was a popular kid, the opposite of a radical extremist,” she said.

Soofi's parents divorced around the time he was in tenth grade, the friend said, and he moved to Utah with his mother.

Over the years, Soofi told his old friends he did not fit in and had many disappointments.

He went to dental school, but said he had to drop out because of financial problems, the male friend said.

He tried and failed at various ventures including a dry cleaning store, he said.

He told friends he had a child with a Bosnian woman but the relationship did not work out.

“He said 'life is really tough here',” the male friend said.

“Alienation, an identity crisis, whatever you want to call it, he was kind of alone.”

“I guess the one thing he could identify with was religion.”

In the past few years, Soofi grew a beard and only posted pictures of himself wearing sunglasses on Facebook, the friend said. Old friends teased him for that but also began to worry, the friend said.

Gradually they lost contact.

“I looked at his pictures, and I didn't recognize him,” the friend said.

“I don't know what happened to him in America.”

The attack was earlier claimed by the extremist militant group Islamic State through a statement made over their Al-Bayan radio. It is the first attack claimed by IS in the United States.

Read more: IS claims responsibility for Texas cartoon attack