Story highlights Authorities apprehend suspect in stabbing, 27-year-old Daniel St. Hubert

Police say St. Hubert was out on parole tied to domestic assault since May 23

Mayor says injured 7-year-old girl "is doing much better"

Prince Joshua "PJ" Avitto, 6, was killed in the stabbing

A New York man arrested in connection with the stabbing of two children in Brooklyn may be linked to another stabbing in a Manhattan subway, a law enforcement official told CNN Thursday.

Police believe Daniel St. Hubert, 27, was out on parole when he stabbed two young children inside an elevator -- killing one of them.

St. Hubert was arrested by detectives around 8 p.m. Wednesday.

He was arrested around the same time that Chief of Detectives Robert Boyce identified St. Hubert by name for the first time as the suspect in the attack.

Detectives were obtaining evidence Thursday that could link him to a fatal stabbing on the subway in the Chelsea neighborhood of Manhattan, the official said.

Investigators were executing search warrants to see if he is linked to additional stabbings since his release from prison on May 23, a law enforcement official said.

Law enforcement has been involved with St. Hubert plenty in the past, including nine arrests, though police did not specify all the outcomes.

The most recent instance was May 23, when, Boyce said. St. Hubert was released on parole in connection to a domestic assault case.

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Nine days later, police believe he encountered 6-year-old Prince Joshua "PJ" Avitto and 7-year-old Mikayla Capers inside an elevator at a public housing complex in Brooklyn. Mayor Bill de Blasio said the two children were "on their way to get ice cream" at the time.

For reasons authorities haven't yet explained, the two children were stabbed -- both in the torso. PJ Avitto was transported to a nearby hospital, where he was pronounced dead.

"These parents are in such pain now," de Blasio said. "... I ask all New Yorkers to help in this investigation any way you can. Do it for this grieving family. Do it for all of us."

Police initially said Mikayla was in critical condition. Speaking Wednesday about her current state, the mayor said, "She's doing much better. She's a strong young lady."

A knife believed to have been used in the attacks was recovered at the scene. A law enforcement official said Wednesday that DNA evidence from that knife helped police identify the suspect. Police Commissioner Bill Bratton, however, added later in the day that police "said nothing about DNA" while insisting forensic evidence more generally helped lead them to the suspect.

As the investigation continues, families of the two stabbed children struggled with the senselessness of the attack.

"Pray for her, and us. And pray for PJ's family. This is senseless. I don't know what monster would do something like this," said Regenia Trevathan, the girl's great-grandmother, to CNN affiliate WCBS

Scott Avitto, PJ's uncle, similarly said the violence "doesn't make any sense."

"We're all just struggling, we're trying to pull it together," he added. "Our family is strong, but we just want justice to be done."

Avitto was related to Taj Gibson, a forward for the Chicago Bulls. Gibson tweeted Monday morning: "They killed my lil super man. #rippj only two more weeks until your 7 birthday. Tears forever." Gibson also posted a picture of Avitto to his Instagram account.

PJ's godfather, Henry Alston, said the boy's funeral will be Friday.

Investigators are considering the possibility the suspect may be responsible for another fatal stabbing that occurred just two days earlier and blocks away.

Tanaya Copeland, 18, was found in the same neighborhood Friday night, unconscious and unresponsive with multiple stab wounds to her torso. Copeland was pronounced dead at a nearby hospital, police said.

The close proximity of the incidents, as well as similarities in the type of weapons used, have led detectives to believe the two cases may be related.

"We have to proceed as if they are aligned," Boyce said. "The knives are very similar. The proximity is four blocks. We have a basic description of the male."