Two men were charged with murder and related offenses Friday in the shooting death of Philadelphia Police SWAT Sgt. James O’Connor IV in Frankford last month.

Khalif Sears, 18, and Bilal Mitchell, 19, were also behind a second-floor door of a rowhouse on the 1600 block of Bridge Street, police said, when Hassan Elliott, 21, fired a rifle through it, striking O’Connor in an arm and shoulder.

In addition to the charge of killing O’Connor, Sears and Mitchell, already in custody in other offenses, were charged after a month-long investigation with seven counts of attempted murder of a law enforcement officer and conspiracy.

Philadelphia District Attorney Larry Krasner and his homicide chief, Anthony Voci, announced the charges during an online news conference Friday afternoon.

O’Connor, 46, died at Temple University Hospital shortly after he was shot about 5:40 a.m. March 13. He had climbed the rowhouse stairs with seven other SWAT team members as they tried to serve an arrest warrant on Elliott, who was wanted in a March 1, 2019, homicide.

Elliott was arrested March 18 and arraigned the next morning on charges of murder, seven counts of attempted murder of a law enforcement officer, and related offenses. He also has been charged with murder and gun and conspiracy charges in the 2019 shooting death of Tyrone Tyree Jr., 33, in Frankford. And he faces attempted-murder and related charges in a December 2019 shooting in Frankford.

Voci said Friday that evidence shows that Elliott was the only shooter and that he fired a .22-caliber assault rifle, fatally wounding O’Connor. Sears and Mitchell were charged with murder under the conspiracy act, and all three are believed to be part of a street gang, Voci said.

Sears was one of two people shot and wounded as police returned fire through the door after O’Connor was shot. Authorities have said 10 guns, eight cell phones, and drugs were found in the house.

Sears last month also was charged with murder and related offenses in the killing of Tyree and has been held at the Philadelphia Industrial Correctional Center.

Voci said that as part of the gang, Elliott, Sears, and Mitchell “conducted a lot of illegal activity that supported each other,” including hindering the arrests of Sears and Elliott while they were on the lam in Tyree’s killing. Authorities believe this behavior culminated in O’Connor’s death, Voci said.

Mitchell, who allegedly was found possessing crack cocaine on March 13, was initially charged with two drug offenses and has been held at the Detention Center on $1 million bail.

Marni Jo Snyder, an attorney for Sears, declined to comment Friday. An attorney for Mitchell did not immediately return a call.

Elliott remains in custody at the Curran-Fromhold Correctional Facility awaiting preliminary hearings. No attorney was listed on his court dockets.

A fourth man who was in the room at the time of the shooting, Sherman Easterling, 24, has been in custody at SCI Phoenix since March 15. At the time of O’Connor’s killing, Easterling was on parole in a 2016 gun-possession case for which he had served state prison time.

Voci said Friday that there is an active arrest warrant for Easterling on weapons offenses in connection with the shooting, but that authorities have not been able to execute it because of the coronavirus pandemic. He said the investigation into O’Connor’s death is continuing.

John McNesby, president of Fraternal Order of Police Lodge 5, said in a statement Friday: “These defendants should have never been on the street, and that led to the murder of a Philadelphia hero, Sgt. Jim O’Connor IV.”

O’Connor, a 23-year veteran of the force, was a married father of two whose family has deep roots in the Police Department. His father is a retired city police officer and his son, James V, is an officer in the city’s Sixth Police District. His daughter, Kelsey, serves in the Air Force.

A week after O’Connor was killed, police led a vehicle procession in Northeast Philadelphia, driving slowly in front of O’Connor’s home as his wife, Terri, stood outside with their children and daughter-in-law. About 200 neighbors, some wearing Irish-green T-shirts with “Philadelphia S.W.A.T.” on the back, also gathered near the home with police officers and Fire Department personnel to watch.

O’Connor was posthumously promoted from corporal to sergeant.

A memorial service at the Cathedral Basilica of SS. Peter and Paul has been delayed by the coronavirus pandemic.