They need to be liberated from Islam

'I absolutely know that in anybody's eyes I was a traitor," says Mosab Hassan Yousef. "To my family, to my nation, to my God. I crossed all the red lines in my society. I didn't leave one that I didn't cross."

Now 32, Mosab is the son of Sheikh Hassan Yousef, a founder and leader of the Palestinian terrorist group Hamas. Throughout the last decade, from the second Intifada to the current stalemate, he worked alongside his father in the West Bank. During that time the younger Mr. Yousef also secretly embraced Christianity. And as he reveals in his book "Son of Hamas," out this week, he became one of the top spies for Israel's internal security arm, the Shin Bet.

For the past two years, Mosab Yousef has lived near San Diego, where he's kept a low profile out of concern for his security. The U.S. is currently weighing his application for political asylum, and until his confession to espionage and the publicity blitz that accompanied it this week, only knew him as the son of a terrorist who sometimes attends evangelical churches in California. The book is intended to launch a new life in America.

Mr. Yousef, whose large, engaging eyes sit prominently on an oval face, says he was confused for many years himself, and realizes many people will be as well. His family has been shamed and old friends refuse to believe him. The book, a Le Carréesque thriller wrapped in a spiritual coming-of-age story, is an attempt to answer what he says "is impossible to imagine"—"how I ended up working for my enemies who hurt me, who hurt my dad, who hurt my people."

"There is a logical explanation," he continues in fairly fluent English. "Simply my enemies of yesterday became my friends. And the friends of yesterday became really my enemies."

The first half of his memoir describes a childhood in Ramallah marked by close familial ties and the Israeli occupation. He describes a kind and unusual Muslim father who cooks dinner, treats his mother well, and cares for his neighbors. An imam trained in Jordan, Sheikh Hassan Yousef rises to prominence in their hometown, and in 1986—along with six other men including the wheelchair-bound cleric from Gaza, Sheikh Ahmed Yassin—forms Hamas at a secret meeting in Hebron. The first Palestinian Intifada—or uprising—breaks out the following year. Mosab did his part, throwing stones at Israeli settlers and army vehicles.

Mr. Yousef traces his awakening to his first sustained exposure to Hamas cruelty. In 1996, he was arrested by the Israelis for buying weapons. He says he was beaten and tortured badly in custody. It was then that the Shin Bet approached him. He says he thought about becoming a double agent. "I wanted revenge on Israel," he writes. But when he was sent to serve his term at the Megiddo prison in northern Israel, he says he was more shocked by the way the maj'd, Hamas's security wing, dealt with other prisoners.

"Every day, there was screaming; every night, torture. Hamas was torturing its own people!" he writes. The Muslims he met in jail "bore no resemblance to my father" and "were mean and petty . . . bigots and hypocrites."

By agreeing to work with the Shin Bet, he got out of prison early. He says he was curious about the Israelis and fast abandoned his idea to become a double agent. Though he took money from Shin Bet and stayed on their payroll for a decade, his handlers in the early years didn't ask much of him. They encouraged him to study and be a model son. His code name was the Green Prince: green as in the color of the Islamist Hamas flag, and prince as the offspring to Hamas royalty.

During those quiet years he met a British cabbie in Jerusalem who gave him an English-Arabic copy of the New Testament and invited him to attend a bible study session at their hotel. "I found that I was really drawn to the grace, love and humility that Jesus talked about," he says in "Son of Hamas."

As a spy, Mr. Yousef wasn't fully activated until the outbreak of the second Intifada in September 2000. A few months before at Camp David, the late PLO chief Yasser Arafat had turned down the Israeli offer of statehood on 90% of the West Bank with East Jerusalem as the capital. According to Mr. Yousef, Arafat decided he needed another uprising to win back international attention. So he sought out Hamas's support through Sheikh Yousef, writes his son, who accompanied him to Arafat's compound. Those meetings took place before the Palestinian authorities found a pretext for the second Intifada. It came when future Prime Minister Ariel Sharon visited the Temple Mount in Jerusalem, site of the Al-Aqsa Mosque and the Dome of the Rock. Mr. Yousef's account helps to set straight the historical record that the uprising was premeditated by Arafat.

Mr. Yousef tells me that he was horrified by the pointless violence unleashed by politicians willing to climb "on the shoulders of poor, religious people." He says Palestinians who heeded the call "were going like a cow to the slaughterhouse, and they thought they were going to heaven." So, as he writes in the book, "At the age of twenty-two, I became the Shin Bet's only Hamas insider who could infiltrate Hamas's military and political wings, as well as other Palestinian factions."

Mr. Yousef claims some significant intelligence coups for himself, and he says he isn't telling the world everything. Early on, he was first to discover that the Al-Aqsa Martyrs Brigades, a terrorist group born during the second Intifada, was made up of Arafat's guards, who were directly funded by international donors. He says he found the most lethal Palestinian bomb maker and foiled assassination plots against President Shimon Peres, then foreign minister, as well as a prominent rabbi. He says he broke up cells of suicide bombers about to attack Israel. And he helped convince his father to be the first prominent Hamas leader to offer a truce with Israel.

His handler—a "Captain Loai," now retired from the Shin Bet—corroborated many of these stories to Haaretz. The paper said the Shin Bet considered Mr. Yousef "the most reliable and most senior agent."

Mr. Yousef strains to justify himself, but ultimately "the question is whether I was a traitor or a hero in my own eyes."

So we're back to why?

The motivation, he says, was to save lives.

"I'd seen enough killing. I was a witness to lots of death . . . Saving a human life was something really, really beautiful . . . no matter who they are. Not only Israeli people owe me their lives. I guarantee many terrorists, many Palestinian leaders, owe me their lives—or in other words they owe my Lord their lives."

He says he used his influence at Shin Bet to get the Israelis to try to arrest Hamas and other Palestinian figures rather than blow them up with missile strikes. He says he saved his father from the fate of Sheikh Yassin and other Hamas leaders whom the Israelis killed by secretly arranging to have him arrested. "I know for sure that my father is alive today, he still breathes, because I was involved in this thing," he says.

Mr. Yousef has some of the evangelist in him, even as he insists he is not a particularly devoted Christian and is still learning about his new religion. He wants Palestinians and Israelis to learn what he did from the Christian God.

"I converted to Christianity because I was convinced by Jesus Christ as a character, as a personality. I loved him, his wisdom, his love, his unconditional love. I didn't leave [the Islamic] religion to put myself in another box of religion. At the same time it's a beautiful thing to see my God exist in my life and see the change in my life. I see that when he does exist in other Middle Easterners there will be a change.

"I'm not trying to convert the entire nation of Israel and the entire nation of Palestine to Christianity. But at least if you can educate them about the ideology of love, the ideology of forgiveness, the ideology of grace. Those principles are great regardless, but we can't deny they came from Christianity as well."

Mr. Yousef says he felt burned out and decided to stop working for the Shin Bet in 2006, against their wishes. He made his way to friends in southern California whom he'd met through bible study.

As the son of a Muslim cleric, he says he had reached the conclusion that terrorism can't be defeated without a new understanding of Islam. Here he echoes other defectors from Islam such as the former Dutch parliamentarian and writer Ayaan Hirsi Ali.

Do you consider your father a fanatic? "He's not a fanatic," says Mr. Yousef. "He's a very moderate, logical person. What matters is not whether my father is a fanatic or not, he's doing the will of a fanatic God. It doesn't matter if he's a terrorist or a traditional Muslim. At the end of the day a traditional Muslim is doing the will of a fanatic, fundamentalist, terrorist God. I know this is harsh to say. Most governments avoid this subject. They don't want to admit this is an ideological war.

"The problem is not in Muslims," he continues. "The problem is with their God. They need to be liberated from their God. He is their biggest enemy. It has been 1,400 years they have been lied to."

These are all dangerous words. Of the threats issued to his life by Islamists, he says, "That's not the worst thing that can happen to you. I'm OK with it, I'm not afraid. . . . Palestinians have reason to kill me. Some Israelis may want to kill me. My goal is not to defeat my enemy. It is to win over my enemy."

Mr. Kaminski is a member of the Journal's editorial board.