18-year-old Devin Morningstar of Moncton has been charged with first-degree murder and arson in connection with death of Baylee Wylie, 18, of Riverview.
Sgt. André Pepin of the Codiac RCMP said Morningstar was arrested in Moncton on Sunday afternoon.
He wouldn't go into detail about the exact evidence that led police to Morningstar.
In court Monday, Morningstar was wearing a grey sweatshirt and stood for the hearing's duration, looking distraught.
His lawyer, Bob Rideout, told Judge Anne Dugas Horsman that he is "concerned about his [client's] mental health."
Rideout asked for a five-day psychological evaluation for Morningstar.
Morningstar will be back in court on Jan 8, 9:30 a.m.
Police had identified two other individuals, Tyler Noel, 18, and Marissa Shephard, 20, as persons of interest in the case on Sunday.
Noel and Shephard remain persons of interest and police are still trying to locate them, said Pepin.
"The investigation has led us to want to talk to these two persons of interest about the victim and what they may know about the circumstances surrounding his death," said Pepin Sunday.
Shephard is described as Caucasian, 167 cm tall and weights 45 kilograms. She has brown eyes and brown hair and has a tattoo with the name Stephen on her neck and a tattoo of a heart on her chest.
Noel is Caucasian with a medium complexion. He is 173 cm tall with a medium build and weighs 64 kg. Noel has brown eyes and black hair, including facial hair and sideburns. Noel has tattoos on his right forearm with the words mom, dad, Mary and a skull.