NEWARK, NJ. (CBSNewYork) — A New Jersey dentist is under investigation after the only child of a couple in their 20s died in his care during a routine procedure.

Prosecutors said 3-year-old Juan Quiej died on Feb. 8 while visiting Dr. Patrick Bamgboye’s office in Irvington.

The 64-year-old dentist is already on probation with the Board of Dentistry for a 2004 incident in which 6-year-old Kyneicha Pagan died in his care at an office in Perth Amboy.

According to a report, a medical examiner found Pagan died of natural causes because she suffered from several serious medical conditions.

The Board of Dentistry reportedly investigated the girl’s death and filed a complaint against the dentist in 2008. Though a judge later found no gross negligence in the case, the board suspended Bamgboye for three months and then placed him on probation for another 21 months.

An attorney for Dental Health Associates told the Star-Ledger of Newark that Bamgboye is cooperating with authorities and it’s too early to assert blame.

Quiej was apparently restrained and under local anesthetic for a routine cavity-filling procedure when he died.

Attorney Joseph Ginarte said Quiej began turning blue in the dentist chair and Bamgboye ignored the mother’s pleas to stop the procedure.

“The mom noticed right away that the kid was not doing well, the he was in distress,” Ginarte said. “She complained to the doctor and said, ‘Stop, my child is not doing well.'”

Ginarte said Bamgboye replied, “Just relax, let me do my work.”

About 15 minutes later, Quiej’s lips apparently began turning purple and his mother complained again.

“He finally realized the child wasn’t breathing,” Ginarte said.

Quiej was taken to the hospital where he was pronounced dead.

The Division of Consumer Affairs, the agency which oversees the Board of Dentistry, is investigating.

The Essex County prosecutor’s office is also reviewing the case and will determine whether a criminal investigation is warranted.

“We received a letter last week from Mr. Ginarte’s law firm advising us of the death of the two children under the care of Dr. Patrick Bamgboye. We will be consulting with the Division of Consumer Affairs, the agency responsible for licensing doctors and investigating charges of non-criminal misconduct. We will then review the case to determine whether a criminal investigation is warranted,”said Acting Essex County Prosecutor Carolyn A. Murray.

Ginarte is pushing for Bamgboye’s license to be revoked.

“Someone like this should not be allowed to come anywhere near our kids, should not be allowed to treat kids under any circumstances” Ginarte said.