Michael Kingsbury (D.C. police)

The body of a child was found late Monday afternoon in Northeast Washington, and police sources said they believed it was the 7-year-old boy with autism who was reported missing over the weekend.

The body, thought to be that of Michael Kingsbury, was found in an automobile behind the 1700 block of West Virginia Avenue NE, where the boy lived.

The cause of death was not known immediately. An autopsy will be conducted.

At a briefing, Assistant Police Chief Peter Newsham said the body of a child who fit the description of the boy the police were searching for was spotted in the car by an officer about 5:50 p.m. Newsham said the vehicle bore no license plates.

The owner of the car was not immediately identified. A police source said that investigators were talking with the owner.

Newsham said it was not clear when the boy had entered the car, and he declined to say where in the vehicle the boy had been found. However, two police sources who spoke on the condition of anonymity because the investigation is ongoing said the body was on the floor of a locked sedan.

Newsham said police were assessing their search, trying to determine whether they had previously looked into the vehicle. Two police sources said that at least one officer had searched the sedan on Sunday. Newsham declined to confirm that account but said that police were looking into it.

Monday’s discovery appeared to conclude a frantic search that traced back to events on Sunday morning.

At 8:30 a.m. Sunday, Michael had been asleep in the bottom of a bunk bed next to an open window covered by a thin drape. Half an hour later, he was playing on the floor. He grabbed a light fixture off a closet shelf and threw it out the window; it shattered when it hit the courtyard below. Michael’s mother said he went after it, exiting a back door that opens from his bedroom and walking down a metal stairway.

The boy — wearing only a pull-up diaper — had not been seen since.

On Monday, more than 24 hours after Michael’s disappearance, police had intensified their search, saturating Trinidad and other neighborhoods off New York Avenue and near Gallaudet University with dogs from Montgomery County, a helicopter, academy recruits and patrol cars.

Police looked through abandoned buildings, including one next to Michael’s apartment, and they concentrated on a back alley where Michael was last seen. Police said they also interviewed known sex offenders who live nearby, which they described as a routine part of their investigation.

Michael’s mother, Katrina Kingsbury, grew more anxious and frustrated, complaining that police were spending too much time talking to her relatives and not enough time searching for her child. She had fliers printed up and was trying to organize a search party even as police blocked off the alley behind her apartment building on West Virginia Avenue and sealed it off with crime scene tape.

“I just want my child back,” she said.

After being reached by telephone Monday night Katrina Kingsbury said she did not wish to speak at that time. “Not right now,” she said.

On Monday afternoon, D.C. police reported no new or promising leads. They confirmed that they were looking into one tip the mother received the previous evening from a woman who phoned to say that she saw Michael on a Metro train playing with colorful pipe cleaners with a heavyset man headed toward Greenbelt. The detail that Michael always clutches pipe cleaners had not been disclosed to the public.

Capt. Lewis Douglas, a supervisor with the youth investigation division, which handles missing-person cases, said detectives were seeking video surveillance footage from Metro to check out the story.

In the meantime, Douglas had said they were concentrating on the last confirmed sighting of the boy, by his older sister, who saw him walking out of the back courtyard and down an alley. “Right now, we have no information that would point us to foul play,” Douglas said, adding, however, “We’re concerned, very concerned.”

Kingsbury said her son was not allowed out without supervision, though he knew how to open the back door. From time to time, he would defy orders but never venture farther than the metal staircase or the edge of the lawn. She said her boyfriend reported him asleep at 8:30 a.m., and her daughter said he was playing in his room at 9 a.m.

But then the sister heard a crash, and when she checked, she saw her younger brother in the back courtyard looking at the fixture that lay broken on the ground. She then saw him walk toward the back alley. She yelled but by the time Michael’s mother reached the courtyard, her son was gone.

By Monday afternoon, off-duty District firefighters had joined the search. And Kingsbury lashed out at police, saying they had questioned her relatives, her mother and her daughter.

“They’re spending all their time interrogating my family,” she said. “They should be out looking for my son.”

Police had said they were investigating every lead and were pouring resources into the search.

Anyone with information is asked to call D.C. police at 202-727-9099 or Youth Investigations Division at 202-576-6768.

Martin Weil contributed to this report.