Osvaldo Rivera, 31, sobbed throughout the hearing on Tuesday afternoon. Action News reporter Vernon Odom said security was extremely tight and Rivera was surrounded by sheriff's deputies.
Rivera is charged with first-degree murder and attempted murder. He was found hiding between a mattress and a bedroom wall Sunday afternoon inside a Camden apartment.
Police also found blood-stained sneakers that matched bloody footprints at the scene of the crime.
Prosecutors say while he was being questioned Rivera told them he had smoked "wet," a combination of marijuana and PCP, prior to the killing.
The 6-year-old boy was found dead with his throat slit in his home on the 900 block of Ware Street about 2:00 a.m. Sunday. His 12-year-old sister also suffered stab wounds and is in critical condition at Cooper University Medical Center in Camden.
Prosecutors say the 12-year-old girl identified her attacker as what sounded like "Poppy." Investigators later determined that Rivera lived in the area and went by the nickname "Popeye."
A nearby resident, Nakyta McCray, told Action News she was able to call 911 Sunday. McCray says the 12-year-old victim rushed out of her home banging on neighbor's doors.
Her throat had been slashed.
"Dispatch asked me 'Was the girl still alive?' I went to the house and saw her sitting there with her throat cut open and barely breathing," McCray said.
Inside the home, Camden Police discovered the girl's younger brother was dead. The killer also slashed his throat.
Two other siblings including a teenager were also in the home; they, however, were uninjured.
"The older sister kept crying that the other two little kids were in the house. I went down to try to get the two little kids, but I seen a bunch of blood, called for officer and he walked in the house and said there was another victim, it was her little brother," McCray said.
The children's mother has been in the hospital recovering from surgery.
The family of the victims tells Action News the 12-year-old was also sexually assaulted. Sunday happened to be the girl's 12th birthday.
Neighbors, meanwhile, are shocked by what happened.
"I can't sleep. It could have been anybody's child, not just her. My prayers go out to the family," said neighbor Karina Mejia.
Authorities say they are extremely concerned about the use of wet in Camden, and they want to get the message out that this is an extremely dangerous drug which has already lead to deadly consequences.