Sayfullo Saipov kept his head lowered — his gaze never met the prosecution’s witnesses who were tearful victims and family members of those who were killed.

Describing their last moments with loved ones before Saipov drove the truck he rented from a New Jersey Home Depot down the Westside Highway Bike Path in 2017.

His attorneys admit he mowed down eight people in the deadly attack and say he was motivated by ISIS propaganda that he wanted to become a martyr for Islam.

Although he did not grow up religious in his native Uzbekistan.

“The radicalization process often starts with somebody who is coming from that position of being, you know, lower on the spectrum of being very religious,” said David Viola, an adjunct professor at the Center on Terrorism at John Jay College.

Viola says the government has a strong case against Saipov — who has pleaded not guilty to 28 counts, including eight counts of murder, 18 counts of attempted murder — and providing support to a terrorist organization.

While Saipov’s own attorneys say he carried out the attack, and still believes in the same ISIS ideologies he did in 2017, they say he had no contact with ISIS officials before the attack but was radicalized by videos shared on social media.

“They have been actually advocating for believers to do exactly what Saipov has. The fact that he doesn’t carry around an ISIS official membership card does not mean that he is not as far as ISIS is concerned part of their movement,” Viola said.

Prosecutors maintain Saipov carried out the attack in order to join ISIS and would have continued to the Brooklyn Bridge if a responding NYPD officer didn’t shoot him, which stopped him in his tracks.

This is the first federal death penalty trial being heard under President Joe Biden, who has previously pledged to eliminate the death penalty at the federal level.

The first phase of the trial will determine if he’s guilty.

If found guilty, the same jury will then determine if he will face an execution.

The trial will resume Tuesday.