A Dorchester man was held without bail today as the third defendant charged in connection with the Sept. 28 slayings of three adults and a toddler on a Mattapan street, Suffolk County District Attorney Daniel F. Conley said today.

EDWARD WASHINGTON (D.O.B. 3/28/79) was arraigned this morning in Dorchester District Court on four counts of murder, one count of armed assault with intent to murder, home invasion, armed robbery, unlawful possession of a firearm, and unlawful possession of ammunition. Because of two prior drug convictions, Washington is charged as a Level II armed career criminal, and the firearm charges come after a previous gun conviction.

Acting on a request by Conley’s chief homicide prosecutor, Assistant District Attorney Edmond Zabin, Judge Rosalind Miller ordered Washington held without bail on the murder charges and revoked his open bail on an unrelated drug case.

Washington’s arrest follows the Oct. 2 arrest of his cousin, KIMANI WASHINGTON (D.O.B. 10/17/75), and the Nov. 22 arrest of another man, DWAYNE MOORE (D.O.B. 6/25/77). Like Edward Washington, Moore is charged with four counts of murder for the Sept. 28 shooting deaths of Levaughn Washum-Garrison, Simba Martin, Eyanna Flonory, and her two-year-old son, Amanihotep Smith, as well as the attempted murder of a surviving victim. Kimani Washington is charged with gun and drug offenses arising out of the same incident.

“This defendant, with co-defendants Dwayne Moore and Kimani Washington, was part of a joint venture to rob people in a home invasion at 23 Sutton St.,” Zabin said. “That robbery and home invasion ultimately led to these murders.”

Martin, who lived at 23 Sutton St., was found in the street when Boston Police responded to shots fired near the intersection of Woolson and Wildwood streets shortly after 1:00 a.m. The other victims lay nearby, with Flonory still clutching her tiny son. A surviving 31-year-old man was rushed to a nearby hospital, where he remains. The information that man provided led investigators to Kimani Washington, Zabin said.

“This defendant met Mr. Moore and Kimani Washington earlier that evening at the home of Kimani Washington,” Zabin said. “He supplied two weapons and drove them to Sutton Street.”

Once at Sutton Street, Moore allegedly took steps to lure Martin outside. Coincidentally, the surviving victim arrived in his own vehicle to meet Martin. The defendants “descended onto the two men and, at gunpoint, forced them to strip and forced them inside.”

Edward Washington was “an active participant” in the robbery that followed and “helped march the victims up the street to where they were shot,” Zabin said. Afterward, he met up with Kimani Washington and Moore to divide the cash, drugs, and other items stolen from the home.

Boston Police arrested Edward Washington yesterday amid an ongoing investigation on the street and behind the closed doors of the Suffolk County Grand Jury. Investigators urged anyone with additional information on the incident to call homicide detectives at 617-343-4470.

Catherine Rodriguez is the DA’s assigned victim-witness advocate. Edward Washington is represented by attorney John Cunha. He will return to court on Jan. 5.