After he was forced to resign as a family medicine doctor amid sexual harassment allegations, he threatened his colleagues. He said he would kill them.
On Friday, Bello returned to Bronx Lebanon Hospital with an AM-15 assault rifle tucked under his white lab coat and opened fire in his old department, killing one doctor and critically wounding six other people at the hospital, according to law enforcement officials.
Bello then shot himself, and staggered, bleeding, into a hallway where he collapsed and died with the rifle at his side, officials said. A photo showed the doctor on a blood-spattered floor as police stood over him.
Now, detectives are trying to piece together what prompted Bello to snap two years after he was forced out, and whether he was hunting for someone in particular when he went to the 16th floor and started shooting.
"There are many, many details that we're still putting together," Mayor Bill de Blasio said, adding that terrorism was not involved in the attack. "This was a horrible situation unfolding in a place that people associated with care and comfort, a situation that came out of nowhere."
His former co-workers described a man who was aggressive, loud, and threatening.
"All the time he was a problem," said Dr. David Lazala, who trained Bello as a family medicine doctor. When Bello was forced out in 2015, he sent Lazala an email blaming him for the dismissal.
"We fired him because he was kind of crazy," Dr. Maureen Kwankam told the Daily News. "He promised to come back and kill us then."
The Daily News reported Saturday that it had received an email purportedly from Bello about two hours before the rampage.
"This hospital terminated my road to a licensure to practice medicine," the email said. "First, I was told it was because I always kept to myself. Then it was because of an altercation with a nurse."
He also blamed a doctor for blocking his chances at getting a chance to practice medicine.
People described a chaotic scene as gunfire erupted, spreading terror throughout the medical facility as employees locked themselves inside rooms and patients feared for their lives after hearing an announcement warning of someone in the building with a weapon.
"I thought I was going to die," said Renaldo Del Villar, a patient who was in the third-floor emergency room getting treatment for a lower back injury.
Shortly after receiving a 911 call about an active shooter, police officers went floor by floor, their guns drawn, looking for the gunman. Fifteen minutes later they confirmed he was dead in the building.
Bello may have doused himself with an accelerant like gasoline and tried to set himself on fire before shooting himself, officials said. Sprinklers extinguished the fire.
The officials were not authorized to discuss the still-unfolding investigation and spoke to The Associated Press on condition of anonymity.
According to New York State Education Department records, Bello graduated from Ross University and had a limited permit to practice as an international medical graduate to gain experience in order to be licensed. The permit was issued on July 1, 2014, and expired last year on the same day. Family medicine doctors handle more routine cases, such as coughs and sprained ankles.
Bello also worked as a pharmacy technician at Metropolitan hospital in Manhattan because he was having a hard time getting licensed as a physician, but quit the job in 2012 and filed for unemployment, according to the lawyer who represented him on appeal in 2014. He lost his case. One former colleague at Metropolitan said he would frequently argue with nurses and bristled at being told what to do, but his attorney in the unemployment action said that's not the man he knew.
"I'm absolutely shocked," attorney David Wim said. "He was such a nice gentleman. He was very humble, very polite, very respectful."
Wim said he even jokingly suggested to his assistant that she date the doctor, who was unmarried.
But Bello had a history of aggressive behavior. In unrelated cases, the doctor pleaded guilty to unlawful imprisonment, a misdemeanor, in 2004 after a 23-year-old woman told police Bello grabbed her, lifted her up and carried her off, saying, "You're coming with me." He was arrested again in 2009 on a charge of unlawful surveillance, after two different women reported he was trying to look up their skirts with a mirror. That case was eventually sealed.
It was not immediately clear if the hospital was aware of his criminal history when he was hired.
Two surgeons at the hospital told the AP that all six victims were in critical condition, but they were expected to survive. Medical staff at the hospital immediately treated all the patients in its emergency department. The victims largely suffered gunshot wounds to the head, chest and abdomen, they said. The most seriously wounded was shot in the liver, said the surgeons, who spoke on the condition of anonymity because they were not permitted to speak publicly.
Employees and their loved ones scrambled for information in the horrifying moments immediately after the shooting.
The 120-year-old hospital has one of the busiest emergency rooms in New York City. It is about a mile and a half north of Yankee Stadium.
In 2011, two people were shot at Bronx Lebanon in what police said was a gang-related attack.
Associated Press writers Steve Peoples and Karen Matthews contributed to this report.
RECOMMENDED FOR YOU