March 16, 2018 06:33 PM

A Florida teen has been accused of stabbing another boy to death during a sleepover earlier this week, in a purportedly planned attack that also left a lawyer and her 13-year-old son with dozens of stab wounds, PEOPLE confirms.

Jovanni Sierra was killed on his 13th birthday early Monday at a friend’s home inside the BallenIsles Country Club, a gated community in Palm Beach Gardens, Florida, authorities revealed at a news conference this week.

Jovanni had his throat slashed as he slept and was stabbed repeatedly, according to officials.

The teen’s suspected killer is 17 and has not been charged as an adult. (PEOPLE does not identify juveniles accused of crimes.)

A grand jury will soon decide whether the older teen should be indicted as an adult on charges of murder and attempted murder. He remains in custody. It was not immediately clear Friday if he has retained an attorney who could comment on his behalf.

Interim Palm Beach Garden Police Chief Clint Shannon told reporters the suspect allegedly confessed to the stabbing attack, which unfolded soon after he awoke early on Monday morning at the home of another friend, who was not harmed.

Shannon claimed that the 17-year-old suspect decided to use a knife he’d brought to the sleepover to kill everyone inside the home. Police said the victims included the suspect’s friend as well as the friend’s mother and 13-year-old brother and Jovanni, who knew the younger brother.

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Jovanni Sierra
Karen Abreu/Facebook

After Jovanni was stabbed, police said the friend’s mom, a family-law attorney, heard moaning coming from upstairs around 6 a.m. Monday and went to check on the boys. As she reached the top of the stairs, they said, the suspect allegedly rushed her and plunged his knife into her body more than 12 times.

She fell down the stairs as her younger son, the 13-year-old, came to her defense, according to police. The suspect then allegedly stabbed him more than two dozen times.

A call to 911 alerted authorities to Monday’s crime scene. The teen suspect was arrested hours after allegedly barricading himself inside the home, according to investigators.

The suspect appears to have been known to law enforcement before Monday’s attack

Shannon said that three agencies — local Jupiter police, the Palm Beach County School District police and the FBI — have all previously investigated the suspected assailant for “alleged violent tendencies” that they received through “intelligence gathering.”

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The suspect’s social media accounts were previously monitored but authorities had no grounds to make an arrest, Shannon said.

The suspect has also allegedly given a series of shifting accounts about his personal and political beliefs.

This week, he allegedly told law enforcement that the 13-year-old boy had teased him about his Muslim faith and Jovanni referenced celebrities as “gods.” The 17-year-old took this as an insult to his religion, he said, authorities allege.

He also said he used the Quran “to give him courage” in the stabbings, police claim.

During the news conference, police also said the suspect and his friend had allegedly watched violent ISIS propaganda videos online hours before the stabbings.

However, in December 2016, the suspect allegedly spoke in seeming support of neo-Nazis and white supremacy, according to the Palm Beach Post, citing a sheriff’s report.

School officials said that in middle school the suspect had allegedly made anti-Semitic and homophobic comments and said his beliefs were in line with the KKK, the Post reports.

At one point his Facebook profile picture was allegedly a swastika, according to the paper.

Jovanni’s mother told the Post her son invited his alleged killer to a pizza party the night before.

“He was my angel for 13 years,” Karen Abreu reportedly said. (PEOPLE was unable to reach her.)

She told the Post, “My son didn’t deserve this.”

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