A Southern California man was found guilty Tuesday of cyberstalking and harrassing the 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, was convicted by a Florida federal jury of interstate transmission of a threat to kidnap and interstate cyberstalking, according to the U.S. Attorney’s Office for the Southern District of Florida.

He used 13 Instagram accounts to target families and friends of the shooting victims, and in some of those messages, he said things like he would kidnap people and that "with the power of my AR-15, you all die," prosecutors said. The gunman in the mass shooting used an AR-15 weapon, authorities have said.

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.

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.

Fleury faces a maximum of 20 years in prison, the U.S. attorney’s office said. Sentencing is scheduled for Dec. 2, according to online court records.

An attorney who represents Fleury declined to comment Tuesday night.