In brief: A California man has been arrested after he used Instagram to harass the families and friends of students killed during the mass shooting at Marjory Stoneman Douglas High School in Parkland, Florida, last year.

Brandon Fleury created Instagram accounts with usernames such as nikolas.killed.your.sister, nikolas.the.murderer, and the.douglas.shooter---references to Nikolas Cruz, who confessed to killing 17 people on February 14 last year, making it the deadliest shooting at a high school in US history. The 20-year-old is awaiting trial and faces the death penalty if convicted.

According to the criminal complaint, Fleury began his campaign of harassment on December 22. "One post threatened to kidnap the message recipients, while others sought to harass the recipients by repeatedly taunting the relatives and friends of the [high school] victims, cheering the deaths of their loved ones and, among other things, asking them to cry," the affidavit said.

The Instagram messages included: "I killed your loved ones hahaha;" "With the power of my AR-15, I erased their existence;" "I gave them no mercy;" and "They had their whole lives ahead of them and I f**king stole it from them."

Instagram handed over the IP address of the accounts after the company was subpoenaed by law enforcement officials. The Washington Post writes that agencies got involved as some of the messages were seen as threats to murder.

On January 16, Fleury was arrested in the Santa Ana home he shares with his father and brother. According to Special Agent Cameron McDowell, Fleury showed no remorse when questioned. He said his actions were a way to "gain popularity," and admitted to having a fascination with Cruz, mass shootings, and serial killers such as Ted Bundy.

Fleury targeted the shooting victims' families because they had allegedly become "activists" and had large social media followings.

Fleury has been charged with online intimidation and harassment and using interstate commerce to threaten kidnapping online.