As legal proceedings move forward against the four defendants charged with participating in the 2009 killing in the basement of Kirkland House, two defendants plan to plead guilty while the two others—the man who allegedly pulled the trigger and the Harvard student who is charged with aiding the murderers—are set to stand trial next month.Prosecutors allege that Jason Aquino, Jabrai Jordan Copney, and Blayn Jiggetts—aided after the fact by Copney’s then-girlfriend Brittany J. Smith, a Harvard student at the time—all entered the basement of Kirkland’s J-entryway with the intent to steal drugs and money from Justin Cosby. The three men then left together once Cosby, a 21-year-old Cambridge resident, had been mortally wounded by the gun they brought.

Yet almost two years later, the legal outlook for each defendant has taken its own trajectory.

THE ALLEGED SHOOTER

The trial of Copney, a New York resident accused of firing the shot that killed Cosby, is set to begin on April 4 in Middlesex Superior Court.

In a hearing yesterday, Superior Court Judge Wendie I. Gershengorn approved motions to allow funds for Copney to contract with an expert on fingerprints, an expert on DNA, and an investigator, according to Copney’s attorney John A. Amabile and court documents.

The court deemed Copney to be indigent in Nov. 2010 and appointed Amabile as his lawyer at that time. Yesterday, Amabile said that since the government may call forensic experts as witnesses, his client needed financial assistance to fund experts who may present an opposing view.

A lawyer familiar with the case posited two avenues on which Copney’s eventual defense may focus—the characterization of the three men’s intentions going into the meeting with Cosby, and the question of who fired the lethal shot.

Court documents allege that when Aquino, Copney, and Jiggetts met Cosby at Harvard on May 18, 2009, Cosby believed the men wanted to buy marijuana from him. But the three New York men all understood that they were going to rob Cosby rather than conduct a transaction with him, the court documents allege.

The lawyer familiar with the Kirkland shooting said that Copney’s defense could hinge in part on a claim that this meeting was indeed intended as a drug deal rather than a robbery.

In addition, the lawyer noted that Jiggetts has testified that he loaded the ammunition into the murder weapon in Smith’s Lowell House dorm room prior to the shooting, possibly linking him rather than Copney to the handling of the gun.

MURDER TO MANSLAUGHTER

Aquino and Jiggetts—the two men who allegedly accompanied Copney from New York to Cambridge and into the basement of the Kirkland annex on the day of the attempted “drug rip”—both plan to plead guilty. In exchange for pleading guilty and cooperating with the prosecution in its case against the other two defendants, the charges of first-degree murder against the men will be reduced to manslaughter.

A first-degree murder conviction entails a mandatory sentence of life without parole in Massachusetts, whereas manslaughter carries a maximum prison sentence of 20 years.

Aquino is expected to plead guilty when he next appears in court this Thursday.

Jiggetts’ intent to plead guilty became evident, according to The Boston Globe, when he took the stand as a witness for the prosecution during a hearing last week. He is expected to change his plea only after he aids the prosecution as a witness in Copney’s trial, according to the lawyer familiar with the case.

Middlesex District Attorney’s Office Spokesperson Cara O’Brien refused to confirm that Jiggetts would plead guilty and noted that at the moment, Jiggetts is scheduled to be tried at the end of April.

EX-STUDENT TO STAND TRIAL

Smith, the final defendant, was a Harvard senior at the time of the shooting. She is scheduled to be tried in May.

Prosecutors say that Copney, who was Smith’s boyfriend at the time, and the other two men used Smith’s Harvard ID to access the basement of the Kirkland annex, where the shooting took place. Court documents further allege that Smith hid the murder weapon in a friend’s dorm room and helped the three men flee to New York by bus after the murder.

In July 2009, Smith signed an agreement with the district attorney’s office that granted her immunity from criminal charges in exchange for her testimony against the other defendants. In March 2010, however, prosecutors said that Smith had intentionally misled investigators, violating the agreement. She was then indicted on six criminal counts, including serving as an accessory after the fact to a murder, unlawfully possessing a firearm, and willfully misleading police and a grand jury.

She appeared in court for a motion hearing last week.

—Xi Yu contributed to the reporting of this story.

—Staff writer Julie M. Zauzmer can be reached at jzauzmer@college.harvard.edu.