Police arrested a 20-year-old East Boston man last Friday for allegedly forcing three women into his car at knifepoint and raping them. Meanwhile, a second individual who has been charged in a fourth attack, was released on his own recognizance due to "new evidence."

Terrance L. Copeland was charged with four counts of rape, three counts of kidnapping, four counts of indecent assault and battery, two counts of assault with a knife, extortion by threat and impersonating a police officer in Dorchester District Court on Tuesday. Copeland allegedly impersonated an officer to intimidate at least one of the victims into silence.

Copeland has been ordered held at $100,000 cash bail until his trial, which has not yet been set.

Suffolk County District Attorney spokesman David Procopio said Tuesday that prosecutors disclosed that DNA evidence collected from the three rapes seem to match the same individual.

"Semen was collected and the DNA have a similar profile," Procopio said. "The DNA has not yet been linked to Copeland."

The arrest follows a massive police effort that was triggered when five young women were abducted and sexually assaulted over the course of a month. Four of the five women- all between 16 and 20 years old- were accosted within blocks of the Ashmont MBTA station.

Copeland allegedly raped the women on Dec. 1, Dec. 28 and Jan 2. In each case, the victims were kidnapped, assaulted and released at a different location. In one case, the victim was raped twice, Superintendent John F. Gallagher said.

Also on Friday, 18 year-old Keyshawn Wallace, who has been charged with kidnapping and attempted rape for a Jan. 3 assault unrelated to the three cases Copeland is charged for, was released on personal recognizance. Wallace was originally held on $150,000 bail, but a spokesman for the Suffolk County District Attorney's office said that "new evidence uncovered indicates that he may not be involved with crime he was charged with."

"The charges remain against him until we can examine the new evidence further," said David Procopio.

Police say they will continue their probe to determine if Copeland is connected to sexual assaults in other city neighborhoods or outside of Boston.

An as-yet unsolved case took place on Jan. 4 and remains under investigation, Gallagher said.

Police are still advising people to use caution while walking from Ashmont station, according to Boston Police spokesperson Mariellen Burns.

(Associated Press reports contributed to this article)