U.S. Attorney William McSwain announced the charges during a Thursday afternoon press conference in Philadelphia.
"We are here to announce that the US Attorney's Office has unsealed an indictment against four individuals...for the murder of Philadelphia Police Sgt. James O'Connor as well as related drug and weapons charges," McSwain said.
The four men are identified as 22-year-old Hassan Elliot, 19-year-old Khalif Sears, 20-year-old Bilal Mitchell, and 25-year-old Sherman Easterling, all of Philadelphia.
McSwain said the four men are alleged members of a drug trafficking group that operates in Frankford, which allegedly obtains and distributes crack cocaine and other controlled substances.
"According to the indictment, all four defendants are responsible for the murder of Sgt. O'Connor," McSwain said.
All four defendants are charged with: murder in the course of using or carrying a firearm during and in relation to a drug trafficking crime; using or carrying a firearm during and in relation to a drug trafficking crime; possession of a firearm in furtherance of drug trafficking; conspiracy to distribute crack cocaine and marijuana; possession with the intent to distribute crack cocaine and marijuana; and maintaining a drug involved premises. Additionally, the indictment charges Elliott and Easterling with possession of a firearm by a felon.
Sgt. O'Connor, 46, was fatally shot shortly before 6 a.m. on March 13 while serving a murder warrant on the 1600 block of Bridge Street in Frankford.
Four days later, the Philadelphia District Attorney Larry Krasner's Office announced murder charges against Elliot.
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Elliot was being sought for a homicide that occurred in 2019. Police said he fired the fatal gunshots.
In April, charges including murder, seven counts of attempted murder of a law enforcement officer and conspiracy, were filed against Sears and Mitchell.
McSwain said the suspects were inside an alleged stash house when Sgt. O'Connor and other members of the Philadelphia Police Department's SWAT team arrived with arrest and search warrants.
McSwain said, as they ascended the staircase to the second floor of the residence and announced their presence multiple times, Elliott allegedly fired a semi-automatic assault rifle 16 times, striking and killing Sgt. O'Connor.
McSwain said the indictment contains a notice of special findings against Elliot which makes him eligible for the federal death penalty.
"(Sgt. O'Connor) literally gave his life to protect the community," McSwain said.
Two other people in the home were wounded by return fire from another officer, according to the D.A.'s office.
The four suspects were ordered held for trial in November on the D.A.'s charges including murder, conspiracy, attempted murder of a law enforcement officer, and weapons offenses.
Their preliminary hearing began a month earlier but was cut short when one of the defense attorneys went into labor inside the courtroom.
McSwain Calls for DA to Step Aside
After announcing the federal charges, McSwain turned in his attention to DA Krasner. He criticized the D.A.'s policies, which he called "pro-violent defendant," and said they were as responsible for Sgt. O'Connor's murder as the suspects.
"Sgt. O'Connor's murder was entirely preventable," McSwain said.
He also blamed the high murder rate and record number of shootings in Philadelphia on the district attorney's actions and inactions.
McSwain called for Krasner to remove himself from the case and let the federal authorities take over.
"It would be absurd, even grotesque, to leave it up to Krasner to direct the prosecution of Sgt. O'Connor's alleged killers," McSwain said.
Sgt. O'Connor's wife of 24 years, Terri, echoed McSwain's feelings on Krasner and told him to step aside.
"His slap on the wrist penalties have caused me a lifetime of sorrow. These males should never have been out of jail. It's time for him to be done and fully release this job to the feds," Terri O'Connor said.
McSwain said no family should ever have to go through what the O'Connor family has experienced over the past nine months.
"We cannot bring their loved one back. But we can honor him by seeking justice," McSwain said. "We promise the O'Connor family, the Philadelphia police department, and the community we will do exactly that."
Family Remembers Sgt. O'Connor
Sgt. O'Connor was a 23-year veteran of the police force and served on the SWAT unit for 15 years.
O'Connor was a corporal at the time of his death and was posthumously promoted to sergeant.
His family was set to honor him with a public viewing and a funeral the following week, but that was postponed because of restrictions on gatherings to stop the spread of coronavirus during the early days of the pandemic.
Nearly two months after he was killed, a funeral was held in May for O'Connor.
The few officers who were able to attend in-person maintained social distancing. Wearing protective masks, they saluted as O'Connor's flag-draped casket was escorted into Our Lady of Calvary Church in Northeast Philadelphia.
RELATED: Family of slain Philadelphia officer speaks out in exclusive interview
His son, James O'Connor V, a Philadelphia police officer himself, delivered a eulogy, remembering his father as a loving man who was dedicated to his family and the community while recognizing the impact of the pandemic.
"This isn't the way we wanted to say goodbye to my father. It's just not fair. When the time is right, we'll give my father a proper send-off," said O'Connor V.
"Everyone knows my father was a Philadelphia police corporal, but he was much more than that. He was a son, a brother, a husband, father, son-in-law, grandfather, and a good friend to many."
Sgt. O'Connor, the son of a police officer, was married to his high school sweetheart, Terri. They raised two children: his son James, the 6th district police officer, and daughter Kelsey, who is in the Air Force.
The couple welcomed their first granddaughter five months before he died.
"One unlucky shot hit him where the vest wasn't at, and my whole life was ruined that morning," Terri told Action News days after her husband's death.
During the March interview, the O'Connor family asked people to honor the father and husband they lost through acts of kindness.
"If someone needs help, go help them because he would do that for anybody at any time. He was there," his daughter Kelsey said.
Philadelphia Police Commissioner Danielle Outlaw posthumously awarded Sgt. O'Connor three medals: The Medal of Honor, Purple Heart, and the Sgt. Robert Wilson, III Medal of Valor.
The Associated Press contributed to this report.