The family of the 6-year-old boy fatally stabbed in an elevator at an East New York public housing development says they are relieved a suspect has been arrested.

But they are far from satisfied by what they have learned so far about the ex-con who has been charged in the horrific attack.

"We just would like to know why," said Scott Avitto, the boy’s uncle. "Why? We just want to know why would you do that to two innocent children?"

Suspect Daniel St. Hubert, 27, was being held without bail Thursday after being charged with the murder of Prince Joshua "PJ" Avitto and the attempted murder of his 7-year-old friend, Mikayla Capers.

No one answered the door at St. Hubert’s last known address in Queens on Thursday. A woman who answered the phone at that address hung up immediately.

The two children were attacked June 1 inside a Boulevard Houses elevator as they were on their way to get ice cream. Capers, bloody and stumbling, walked out of the building, according to court records. She slipped and fell just as authorities say St. Hubert fled from the housing complex.

Capers, who was stabbed more than a dozen times, is recovering at New York-Presbyterian-Columbia University Medical Center. "She's still fighting for her life," Avitto said.

The investigation into the attack was complicated by the lack of security cameras inside the public housing complex, which led to criticism from the mayor and police.

Police circulated a sketch of the suspect to the media and made appeals to the public for help. Police started looking at St. Hubert after his blood was allegedly discovered on a large knife recovered from the scene of the stabbings, according to court records. The suspect was picked up in South Ozone Park Wednesday night.

Police are also questioning St. Hubert about the attack of 53-year-old Kyle Moore, who was stabbed multiple times in his torso on the southbound platform of the 18th Street No. 1 station Wednesday. Police said Moore had gotten into an argument with several people before the 5:30 a.m. attack. He was taken to Bellevue Hospital Center in stable condition. No weapon was recovered, police said.

And police say St. Hubert has not been ruled out as a suspect in the stabbing death of 18-year-old Tanaya Copeland on May 30. Copeland, an LIU Brooklyn student and aspiring nurse, was found stabbed more than 30 times on an East New York street just a few blocks away from the housing development.

Mayor Bill de Blasio called St. Hubert “the most likely suspect” in the death of the 18-year-old, but said there is not enough evidence yet to charge him in that case.

Chief of Detectives Robert Boyce said St. Hubert “a dangerous individual” who had been released on parole last month for a domestic assault and has nine prior arrests. He has been accused of assaulting a police officer and corrections officer, Boyce said.

St. Hubert was convicted of attempted murder in the second degree in June 2012, according to court records.

On Thursday, the police sketch of St. Hubert still lined the streets near the housing complex where the kids were attacked on Schenck Avenue. A memorial for PJ had grown to dozens of candles, stuffed animals and Spider-Man balloons.

“For that to happen here is horrific,” said Jeannette Moore, 58, who lives in the housing complex and works as a crossing guard nearby. “We feel a little bit safer now, but my heart goes out to the children.”