BALTIMORE — Paul Warren Pardus spent restless nights with his ailing mother at Johns Hopkins Hospital, and when he believed doctors had failed her, he decided he would determine her fate.

The 50-year-old, distraught over his mother’s medical condition, shot her physician on a top floor Thursday morning at Johns Hopkins Hospital before turning the gun on his mother and himself. The doctor survived, the man and his mother did not.

Pardus had spent much of his time at the hospital since last week, where his 84-year-old mother Jean Davis had undergone surgery related to cancer treatment. When Dr. David B. Cohen delivered bad news, Pardus pulled a semi-automatic handgun from his waistband, shot Cohen in the abdomen and ran into her hospital room.

A four-hour standoff ensued, in which some parts of the sprawling East Baltimore campus were locked down and others were evacuated. Snipers took to the roofs, as people in surrounding buildings were ordered away from windows and to draw the blinds.

In the end, investigators believe Pardus and Davis were dead the whole time. After sending in a robot with a camera, they discovered the bodies — the bedridden Davis with a gunshot wound to the back of the head, Pardus on the floor, shot through the mouth.

Several Hopkins personnel, some who worked on the eighth floor of the Nelson building, said that Pardus blamed Cohen for paralyzing his mother during surgery. According to one witness who spoke with detectives, he yelled, “”You ruined my mother.””

“”He thought it was (the doctor’s) fault, but it wasn’t,”” said a nurse, who did not want to give his name because staff at the hospital was discouraged from discussing the incident with news media.

Little was known about Pardus, a resident of Arlington, Va. He had identified himself to hospital staff as Warren Davis, his middle name and mother’s last name. Records show he had a permit to carry a concealed weapon in Virginia, and he did not appear to have a criminal record beyond traffic violations.

In 1998, he filed for Chapter 7 bankruptcy, and a website lists him as the holder of a copyright for a screenplay and lyrics to a song called “”I Love the Lord.””

His mother and other relatives appeared to live in rural Virginia.

By mid-afternoon, floors of the Nelson building had been evacuated and the police perimeter around the hospital had extended. Police were shuffling groups of people away — some police officers even pushing patients in wheelchairs away from the scene themselves — and employees were visibly shaken and calling family members as they hurried away from the scene.

Michelle Burrell, who works at a coffee bar in the hospital lobby, said that she communicated via text message with a friend in a room on the eighth floor of the Nelson building shortly after the shooting. She and others had locked themselves in a room.

“”She just let me know she was safe, and that’s all I was worried about,”” Burrell said. She said the scene in the lobby of the hospital was chaotic, with people running for cover, locking themselves in rooms.

Jacqueline Billy, a nurse who works in respiratory care, was on the seventh floor and got an elevator that took her up to the eighth. She was greeted by police, guns drawn, who ordered her to shut the door.

“”I was petrified, the door opened and there are a bunch of guns. You never expect that,”” she said.

Police Commissioner Frederick H. Bealefeld said that tactical teams, which included the Baltimore city police and SWAT teams, the FBI, and Baltimore County SWAT teams were called in, and had set up a command center within 45 minutes after the incident.

“”By all evaluations, everything worked as designed,”” Bealefeld said.

In the School of Nursing across the street, students sat in a computer room and study lounge, speaking in hushed tones about the scene unfolding across the street.

A group of students, peering through the blinds, noted that large X’s had been placed in several windows, presumably to note those rooms that were clear. One girl read aloud a text message that said the doctor had died, information that would prove incorrect.

Amy Wilson, wearing purple hospital scrubs, sat on the floor of the nursing school’s main lobby, beneath a flat-screen TV notifying students of a “”shooting incident”” and instructing them to stay tuned for updates. A member of the support staff in the intensive care unit, Wilson said staffers often have to call security or police when fights break out among family or others visiting the hospital. But she had never heard of such an attack on a medical professional.

“”It’s a scary reality”” of working at a big institution, said Ashley Salamone, also a nurse in the intensive care unit.

Cohen was reported to be in stable condition as of Thursday night. Those who work with him said he was a well-liked and respected orthopedic surgeon who has worked at the hospital for more than a dozen years and was known for performing magic tricks. A Hunt Valley, Md., resident, they said he was a father of two whose wife also worked at Hopkins, as a nurse.

Ashley Davis, an emergency room employee, said that she saw Cohen as he was rushed off to surgery. “”By the time I saw him, he was on a stretcher and people were all around him,”” Davis said, adding that she didn’t see any blood, and that Cohen appeared to be conscious. When asked to describe the scene in the emergency room, she just said, “”It was frightening.””

Mayor Stephanie Rawlings-Blake commended the rapid response of law enforcement officials, saying that she was “”very troubled by the incident,”” but that, “”the safety and security of Johns Hopkins employees was paramount throughout this whole incident.””

“”Hopkins is the best medical institution in the world and this incident, as tragic as it is, is not going to change that,”” Rawlings-Blake said.

Although Hopkins has long made safety a priority at its medical campus in East Baltimore, located in one of the city’s most dangerous areas, the hospital does not require patients or visitors to pass through metal detectors. An exception is the Emergency Department, where guards conduct searches and wave a metal-detecting wand over visitors.

Metal detectors are rare in American hospitals, and security experts say they are generally not feasible or desirable.

“”We’re trying to strike a balance to make our institutions warm, open and inviting, and at the same time protecting everybody who comes through,”” said Joseph Bellino, president of the International Association for Healthcare Security & Safety, a professional organization based in Illinois.

“”Most of the time we do a very, very good job,”” he said. “”Every now and then we get these events that are anomalies.””

Police are not sure when Pardus shot himself and his mother. Anthony Guglielmi, the department’s chief spokesman, said there were no witnesses who heard the gunshots. After he was shot, Cohen collapsed outside the doorway, and the shooter barricaded him and his mother in the room.

“”He was last seen running into the room, brandishing the handgun in the direction of his mother, who was confined to the bed,”” said Bealefeld.

He said police had not communicated with Pardus at any point, and investigators believe the shooting was swift. The robot camera showed the bodies, at which point police communicated, “”Subject shot.”” That led police to initially report police had shot Pardus, which they later corrected.

It was not clear just how grim the news delivered by Cohen to Pardus was, but Pardus decided a quick death was the only resolution. Investigators believe he shot her in the back of the head so she would not see it coming – a “”mercy killing,”” as one veteran officer described it.

“”It was sad,”” said one official who viewed the scene.