The hardest thing for a cop to do is go after another cop.

And when cops have to do it, they rarely want the publicity that typically accompanies an important bust.

Detective Shawn M. Reichenberg Sr. got the electronic equivalent of a framed commendation — recognized in a Twitter note and in an e-mailed news release hours after he charged a fellow officer in the fatal shooting of an unarmed man outside a club in Mount Vernon.

Police Commissioner Frederick H. Bealefeld III said in a brief statement that the first-degree murder and other charges against the officer "are an aberration and affront to us all" while he also thanked the detective "who literally worked around the clock since the onset of this investigation."

The tribute is tempered.

"This is going to be tough on him," said Robert Cherry, president of the police union and a former homicide detective who got to know Reichenberg back when he pushed a patrol car in Northwest Baltimore more than a dozen years ago.

"He's one of those guys who wouldn't hesitate to back up another police officer," Cherry said. "He takes his job very seriously, and his integrity is beyond reproach."

Reichenberg, who is approaching 18 years on the force, three of them in homicide, is fighting another battle as well — this one tragic and personal — at his Anne Arundel County home.

His teenage son, Shawn M. Reichenberg Jr. has Hodgkin's lymphoma and is struggling. The Pasadena community has rallied to raise money for the boy's medical care and classmates at Northeast High School have banded together to help.

Cherry said the homicide detective, who deals with untimely and violent deaths every day while at work, "hasn't given up hope" for his son, "yet he continues to do his job."

Citing the high-profile investigation of the shooting by Officer Gajihi A. Tshamba, police commanders would not allow Reichenberg to be interviewed. Other detectives and friends in the department likewise would not comment.

Prosecutors who work closely with homicide detectives also wouldn't talk. A spokesman for the State's Attorney's Office said it would be inappropriate to discuss "the talents, professional abilities and personal traits" of a detective involved in an open case.

Reichenberg is what is called in Baltimore vernacular a "Murder Police," a reverence the close fraternity of detectives grant themselves as those who speak for the victims who can't speak for themselves.

They rotate shifts and take cases as they come in from dispatch. At any given moment, the detective who is "next up" could find himself at the unattended death of an elderly woman, a suicide, a drug killing in an alley or a body floating in the harbor.

On the Saturday of June 5, at 1:30 in the morning, it was Reichenberg's turn to answer the phone.

Almost immediately the detective was thrust into a case with intense public pressure, internal scrutiny, sensational headlines and daily leaks that splattered some of the most intimate details into the headlines. The off-duty Tshamba, offended that another man had patted his female companion's rear end, had shot the offender, a former Marine, a dozen times in the chest and groin.

Tshamba didn't make a statement nor did he submit to a breath test to determine whether he had been drinking. His lawyer now says the officer put himself on duty to investigate a sexual assault and shot after being threatened. Police officials have said there is no evidence of a physical confrontation and that the victim had his hands in the air when the officer opened fire.

Reichenberg's bosses deemed the shooting unjustified almost from the start, adding to a sense of urgency, and police officials pressed prosecutors to allow them to make an arrest quickly.

Friday night, less than a week after the shooting, prosecutors gave Reichenberg the green light to obtain an arrest warrant charging Tshamba, sparking a 30-hour manhunt when the officer failed to surrender. The officer turned himself in early Sunday at the booking center.