The only person arrested in the shooting deaths of four people — including a 2-year-old boy — had one of the murder weapons and a victim's car, and other people are believed to have been involved, a prosecutor said Wednesday.

Kimani Washington, 34, was ordered held on $500,000 cash bail after his arraignment in Dorchester District Court on charges of weapons violations, receiving a stolen car, drug trafficking and being a career criminal. Not guilty pleas were automatically entered on his behalf.

No one has been charged with murder in the case. Prosecutor Ed Zabin said the investigation is "ongoing and comprehensive," and more charges may be filed.

Washington was arrested Oct. 1 in Manchester, N.H., three days after five people were shot in Boston's Mattapan neighborhood.

Zabin said Washington admitted in a recorded interview with police that he drove one of the victims' rental car shortly after the murders. He also admitted to possessing two guns, both found during a search of his mother's apartment, Zabin said. One of the guns was used in the killings, the prosecutor said.

Killed in the shootings were 2-year-old Amani Smith; his mother, 21-year-old Eyanna Flonory; her boyfriend, 21-year-old Simba Martin; and 22-year-old Levaughn Washum-Garrison. The fifth victim, 32-year-old Marcus Hurd, remains hospitalized in critical condition.

Hurd told police before he lost consciousness that the people who shot him had taken his rental car, a Ford SUV, Zabin said.

Washington did not speak at Wednesday's hearing, which was packed with friends and relatives of the victims. His lawyer, John Salsberg, has said he "unequivocally denies" hurting anyone.

Zabin asked for $1 million cash bail, citing Washington's lengthy criminal record, including previous convictions on charges including drug trafficking and assault and battery. He also said Washington had a large amount of crack cocaine in the rental car.

In making his argument to hold Washington on a high bail, Zabin cited "some additional charges which may be forthcoming." He did not elaborate.

There were audible sobs in the courtroom when Zabin described how victims were found in the street shortly after 1 a.m. on Sept. 28 — some of them naked — with Flonory lying on a sidewalk clutching Amani.

Salsberg said he was not making an immediate argument on bail because prosecutors had not provided him with their recording of Washington.

Zabin said prosecutors did not want to turn it over to the defense before a grand jury investigation, "particularly in a case where there is a suggestion that other people are involved."

Outside court, Salsberg said his client was glad to be back in Massachusetts to face the charges. "Mr. Washington's family and friends remain very supportive of him," the attorney said.

Judge Rosalind Miller set a probable cause hearing for Nov. 5.