A 33-year-old man shot and critically injured his mother and stepfather Tuesday morning inside the home where all three lived on a quiet cul de sac in Waldorf, then retreated to an upstairs bedroom where he shot and killed himself, authorities said.

When Charles County sheriff’s deputies finally entered the house in the 3500 block of Seagrape Court — about four hours after the man’s mother first called to report trouble with her son — they found Shea Proctor dead of a gunshot wound with a revolver lying near his body, authorities said. Emergency responders had already taken his mother and stepfather to the hospital, having found them shot and lying in the street outside when they first arrived at the scene, authorities said.

“It’s a quiet neighborhood, nice homes, just a very quiet street,” said Diane Richardson, a spokeswoman for the Charles County Sheriff’s Office. “I think it’s a bit shocking for neighbors. Things just don’t happen that often.”

The trouble began shortly after 5 a.m., when Proctor’s mother dialed 911 to report trouble with her son, Richardson said. Proctor, she said, had come into the bedroom where his mother and stepfather were sleeping and started arguing with them. The argument escalated, she said, and Proctor shot both of them inside the home, Richardson said.

Richardson said the mother, whose age she did not know, and stepfather, 48, were able to make their way outside, running in opposite directions before they collapsed in the street in the Sentry Woods subdivision. Proctor, she said, did not leave, and sheriff’s deputies and others arrived thinking he might still be armed and inside his home.

“They had no idea if that shooter was still inside the house, no idea if he was still alive, still armed, and they could be fired upon,” Richardson said.

Richardson said deputies and emergency responders immediately moved Proctor’s mother and stepfather from the area and flew them to a nearby hospital, where they remained Tuesday afternoon in critical but stable condition. Deputies on the sheriff’s emergency services team then warned neighbors to stay indoors as they called in a hostage negotiator and tried to contact Proctor, Richardson said.

About 9:15 a.m., Richardson said, deputies went inside and found Proctor dead in the upstairs bedroom of an apparently self-inflicted gunshot wound.

It remains unclear why Proctor was arguing with his mother and stepfather, Richardson said. She said that Tuesday afternoon, investigators were hoping that his mother’s condition might improve to the point where she could talk to her about the incident. She said they also were researching whether they had ever previously been called to the home.

Richardson declined to identify the mother and stepfather because they are crime victims.

Online court records show Proctor has had several previous run-ins with law enforcement. He was convicted of second-degree assault in Prince George’s County in 2009, the same year he was convicted in Charles County of driving while impaired by alcohol and driving on a suspended license, the records show. He was also convicted of driving while under the influence in Charles County in 2008, and he was convicted of another second-degree assault charge in Prince George’s County in 1999, the records show.