UPDATED 5:15 P.M.
NEW YORK—Massachusetts and New York police have arrested a third man in connection with the May 18 Kirkland House shooting that left one Cambridge resident dead, prosecutors announced Friday.

Jason Aquino, 23, of Manhattan, was arrested at roughly 4 p.m. Thursday at his home in Harlem on charges of first degree murder, accessory after the fact of murder, armed robbery, and possession of a firearm. He was arraigned in Manhattan Criminal Court Friday afternoon on a fugitive affidavit and has agreed to waive extradition and return to Massachusetts to face charges.

"We now have in custody all three men who we believe were involved in the shooting death of Justin Cosby," Middlesex District Attorney Gerry Leone said in a press release. "I want to commend the excellent, cooperative investigation conducted by the Massachusetts State Police, Cambridge Police, and Harvard University Police. I also want to thank the New York City Police Department for their cooperation and tremendous assistance in identifying and locating the defendants in this case."

After the arraignment, Massachusetts police officers escorted a handcuffed Aquino out of the court in an emotional scene. Aquino's family sat in the back row of the courtroom and his teary-eyed mother asked reporters to "please say nothing to us."

Corey Welford, a spokesman for the District Attorney's office, said that a definitive date has not been set for Aquino's arraignment at the Cambridge District Court, but added that it could happen as soon as Monday.

Aquino's arrest comes little more than a week after Jabrai J. Copney, 20, also of New York City, was arraigned in Middlesex Superior Court and pleaded not guilty to all five of the charges he faced in connection with Cosby's death. Copney, who turned himself in to police on May 21 and has since been held without bail, has been charged with all four of Aquino's crimes, as well as attempt to commit a crime. Welford said he could not comment at this time as to why Copney faces the additional charge.

Copney's defense attorney, J. W. Carney, Jr., said after last Wednesday's arraignment that he has yet to see "any evidence whatsoever" from the Commonwealth indicating that his client was "a participant in the murder." Carney also noted that Copney—who he said was in a "surprisingly good" mood—is a Christian and prays each morning and evening.

"He really does believe that God has a purpose in having him charged with this crime," Carney said after the arraignment. "He doesn't know what that purpose is yet, but he is confident it will turn out all right for him."

A second suspect, Blayn "Bliz" Jiggetts, 20, of Mount Vernon, N.Y., was arrested on June 9 in connection with the shooting. Jiggetts, who refused to return voluntarily to Massachusetts to face charges and is currently jailed without bail in New York, was indicted Thursday by a Middlesex grand jury on the same charges as Aquino, allowing his case to be heard in Middlesex Superior Court. An arraignment date for Jiggetts has not yet been set, and Welford said that prosecutors are continuing to seek a governor's warrant, which requires the signatures of both the Massachusetts and New York governors, to extradite Jiggetts.

Aquino, Copney, and Jiggetts—none of whom were Harvard students—allegedly participated in what investigators have called a failed "drug rip" that left Cosby, 21, dead. Shots were fired, and Copney, Jiggetts, and Aquino fled the scene and returned to New York City via bus that evening, investigators say. Four ounces of marijuana, wrapped in a "bloody work shirt," were found near Cosby after the shooting.

Copney was seen leaving Kirkland House immediately after the shooting carrying a gun, police say. That weapon, a 9 mm semiautomatic pistol, has been recovered and determined to have been in Copney's possession immediately after the murder. A report of the incident by prosecutors says that the pistol was of the same caliber as casings found at the scene, and a jacket worn by Copney the day of shooting also tested positive for gunshot residue.

Welford, the spokesman for the District Attorney's office, said that prosecutors believe these are the three individuals that were involved in the shooting, but that investigators are continuing to look into the matter. Welford said that the three men were "known to each other," but he would not speculate further on their relationship before the shooting.

—Staff writer Peter F. Zhu can be reached at pzhu@fas.harvard.edu.
—Staff writer Bonnie J. Kavoussi can be reached at kavoussi@fas.harvard.edu.