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A Southern California man was sentenced Monday to more than five years in prison for cyberstalking and harassing families and friends of victims of the 2018 mass shooting at Marjory Stoneman Douglas High School in Parkland, Florida.

Brandon Michael Fleury, 22, of Santa Ana in Orange County, was convicted by a federal jury in Florida in October of interstate transmission of a threat to kidnap and interstate cyberstalking.

He used 13 Instagram accounts to target victims' families and friends and sent messages that threatened kidnapping and violence, prosecutors said. Among the messages he sent was one that read "with the power of my AR-15, you all die," prosecutors said. The gunman in the mass shooting that killed 17 people used an AR-15 weapon.

While Fleury was sentenced to 66 months in prison, six of those months will run concurrently, or at the same time, to a 60-month sentence, the U.S. Attorney’s Office for the Southern District of Florida said in a statement.

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Nikolas Cruz, now 21, is accused of killing 17 people, mostly students, at the high school on Valentine's Day 2018. Prosecutors have said they will seek the death penalty.

In some of the messages, Fleury used aliases that included Cruz as well as serial killer Ted Bundy, prosecutors said. Fleury was charged in January 2019.

Fleury told law enforcement officials that he posted the messages "to taunt or 'troll' the victims and gain popularity" and notoriety online. He said he targeted family members who he considered "activists," according to a criminal complaint.

Since the shooting, several survivors have called for gun control and become leaders in anti-gun campaigns.

There was testimony at Fleury's trial that he is autistic, although several mental health experts said he did understand right from wrong.

His attorney, Sabrina Puglisi, said she had hoped the judge would give greater weight to his mental issues in imposing a sentence.

"I think that it’s a high sentence given Brandon’s background and other similarly situated cases, but I believe that the judge felt the need to have the sentence send a message to others that are out there on the internet doing this bad behavior," Puglisi said.

Prosecutors sought the maximum sentence of 20 years. They said in court documents that some of his victims believed Fleury lived in Parkland.

"The victims lived in constant fear that the individual bombarding them with this vile messages sought to follow in Cruz’ footsteps," prosecutors wrote in seeking the maximum sentence. They also said that he knew they were grieving and in pain, but "he just did not care."