NEW YORK (CBSNewYork/AP) — A 19-year-old former student suspected of killing more than a dozen people at a Florida high school was the adopted son of a former Long Island couple.

Police said Nikolas Jacob Cruz opened fire with a semi-automatic weapon on Wednesday afternoon at Marjory Stoneman Douglas High School, killing 17 people and sending hundreds of students fleeing into the streets.

More details are starting to emerge about the alleged gunman a day after the shooting.

Cruz and his biological brother were adopted by Lynda Cruz and her husband after the couple moved from Long Island to Broward County.

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His father died of a heart attack more than a decade ago. Those who knew the teen said he was very troubled and seemed to have gotten worse since his mother’s recent death.

His mother died in November of complications from the flu, WCBS 880’s Marla Diamond reported.

Lynda Cruz’s sister-in-law, of Long Island, told the Sun Sentinel that she only met the boys once when they came to New York to attend a family funeral. She said they were very young at the time.

Cruz and his brother were left in the care of a family friend after their mother died, the Sun Sentinel reported.

But Cruz reportedly wasn’t happy and eventually moved in with the family of a friend he knew from the school.

An attorney for that family told the Sun Sentinel that they’re devastated and “didn’t see this coming.”

On Thursday, the leader of the white nationalist group, the Republic of Florida, said Cruz was a member of his group and participated in paramilitary drills in Tallahassee.

Jordan Jereb told The Associated Press that his group wants Florida to become its own white ethno-state. He said his group holds “spontaneous random demonstrations” and tries not to participate in the modern world.

Jereb said he didn’t know Cruz personally and that “he acted on his own behalf of what he just did and he’s solely responsible for what he just did.”

He also said he had “trouble with a girl” and he believed the timing of the attack, carried out on Valentine’s Day, wasn’t a coincidence.

(© Copyright 2018 CBS Broadcasting Inc. All Rights Reserved. The Associated Press contributed to this report.)