A former New York stock broker who fled his job and family to fight alongside Islamic State militants in Syria, then maintained his allegiance to the extremist group throughout his trial, was sentenced to life in prison on Tuesday.

Ruslan Maratovich Asainov, who served as a sniper and instructor for the Islamic militant group at the height of its power, sat grinning in the Brooklyn courtroom, flashing a thumbs-up and stroking his bushy beard as a judge read out the sentencing.

His own court-appointed attorney, Susan Kellman, declined to ask for a lighter sentence, noting her client was not interested in distancing himself from the Islamic State fighters in exchange for leniency.

“It’s rare that I start my remarks at sentencing by saying I agree with the government,” Kellman said. “This is who he is. This is what he believes, fervently.”

Asainov, a 47-year-old U.S. citizen originally born in Kazakhstan, was living in Brooklyn in late 2013 when he abandoned his young daughter and wife to fight alongside the Islamic State group in Syria.

After receiving training as a sniper, he participated in pivotal battles that allowed the militant group to seize territory and establish its self-proclaimed caliphate based on a fundamentalist interpretation of Islamic law. He rose to a rank of “emir,” or chief, then taught more than 100 aspiring snipers, acting as a “force multiplier" for the Islamic State group's "bloody, brutal campaign,” according to prosecutors.

Asainov told law enforcement officials that he did not recall how many people he had killed. But he spoke proudly of participating in the violent jihad, bragging that his students had taken enemy lives.

“He chose to embrace killing as both a means and an end,” Matthew Haggans, an assistant United States attorney, said during the sentencing. “He holds on to that foul cause today.”

Asainov did not participate in his own trial, refusing to stand for the judge or jury. Inside the Brooklyn jail cell, he hung a makeshift Islamic State flag above his desk and made calls to his mother on a recorded line describing his lack of repentance.

Asainov was convicted earlier this year of providing material support to a foreign terrorist organization and causing at least one death, among other charges. He is one of dozens of Americans — and thousands of foreign fighters worldwide — who have heeded the calls of the Islamic State militants to join the fighting in Iraq and Syria since 2011.

Mirsad Kandic, a Brooklyn resident who recruited Asainov and others to join the Islamic State group, was sentenced to life in prison this summer.

During Asainov’s trial, his ex-wife testified that he had once doted on their young daughter. But around 2009, she said, he became consumed by extremist interpretations of Islamic Law, quitting his job as a stock trader, throwing out his daughter’s toys and forbidding his wife from putting up a Christmas tree.

In late 2013, he boarded a one-way flight from New York to Istanbul, ultimately arriving in Syria with the help of Kandic. He maintained occasional contact with his wife, bragging about his connection to the “most atrocious terrorist organization in the world” and warning that he could have her executed.

He was captured in 2019 by Syrian Democratic Forces during the Islamic State group’s last stand in a tiny Syrian village near the border with Iraq, then turned over to the United States.

In their sentencing memo, federal prosecutors said Asainov should face the maximum sentence of life imprisonment for both the nature of his crimes and the fact that he has not shown “an iota of remorse, doubt, or self-reflection on past mistakes.”

On Tuesday, Judge Nicholas Garaufis said he agreed with prosecutors.

“Its hard for the court to have any understanding or sympathy for what we have seen in this trial,” he said.