Authorities today announced the arrest of a second man on murder charges for the deaths of three adults and a child on Woolson Street in Mattapan on Sept. 28.

Edward Washington, 31, of Dorchester, is a cousin of Kimani Washington, whom authorities charge participated in the drug shakedown and robbery that led to the murders.

Last month, police charged Dwayne Moore, 33, of Mattapan, with the four murders.

In addition to the murder charges, Edward Washington will face charges of armed assault with intent to murder, home invasion, armed robbery, and unlawful possession of a firearm, when he is arraigned in Dorchester District Court, likely tomorrow, the Suffolk County District Attorney's office says.

In 2006, Edward Washington was acquitted on federal racketeering and conspiracy charges related to his alleged involvement in the Esmond Street Crew, a violent gang that authorities said attempted to murder members of the rival Franklin Hill Giants partly for status, but mostly to protect its cocaine business in the Esmond Street area in 2000 and 2001.

A federal judge ordered Washington and a co-defendant not guilty the day after the jury declared itself deadlocked, over the issue of whether the gang was organized enough to be tried under federal racketeering laws.

In the federal case, Washington was accused of shooting at a Franklin Hill gang member on Sept. 16, 2000.