Some messages were sent on Instagram from the username “the.douglas.shooter.”

A 22-year-old California man was sentenced to 66 months in federal prison on Monday for cyberstalking and sending a kidnapping threat to families of the victims in the Parkland, Florida, school shooting.

Brandon Fleury used 13 Instagram accounts — which had aliases including alleged Parkland gunman Nikolas Cruz and serial killer Ted Bundy — to target Parkland victims’ families and friends, federal prosecutors in Florida said.

Fred Guttenberg, whose 14-year-old daughter, Jaime, was killed in the Parkland shooting, in a tweet called this “a precedent setting case that will give the FBI and DOJ [Department of Justice] additional tools to prosecute harassment going forward.”

Jaime Guttenberg was among the 17 students and staff shot dead at Marjory Stoneman Douglas High School on Feb. 14, 2018, allegedly by Cruz, a former student.

In one message, Fleury wrote, “With the power of my AR-15, you all die,” according to prosecutors. Another said, “With the power of my AR-15, I take your loved ones away from you PERMANENTLY.”

Another message said, “I’m your abductor I’m kidnapping you fool,” according to prosecutors.

The cyberattacks lasted from December 2018 to January 2019, prosecutors said. Some of Fleury’s messages had Cruz’s profile photo, prosecutors said.

Fleury was convicted in October of interstate transmission of a threat to kidnap and interstate cyberstalking, prosecutors said.

Fleury’s attorney, Sabrina Puglisi, told ABC News on Tuesday that her client is an “autistic young man who has the social and emotional functioning of a child.”

Prosecutors had sought a 20-year sentence which Puglisi called “so unreasonable that it is offensive.”

“I understand the judge’s need to send a message that this type of behavior on social media will not be tolerated, but Brandon doesn’t deserve to be in prison for five years,” she said.

Cruz is at the Broward County Jail awaiting trial.