S. Randolph Sengel has been Alexandria’s chief prosecutor for 16 years. (Lucian Perkins/The Washington Post)

When S. Randolph Sengel retired last week as Alexandria’s commonwealth’s attorney, he packed a photograph that now sits on his desk at home. It’s of Katelynn Frazier, a 3-year-old who was beaten to death by her mother’s boyfriend while in city custody 13 years ago.

“Those kinds of cases just tear you up,” he said recently while cleaning out his office after 16 years as the city’s top prosecutor. “I felt like it was something that was preventable, and it shouldn’t have happened, and it was a wake-up call.”

Sengel, 64, personally tried the case against the boyfriend, one of several high-profile killings and police shootings his office handled during his four terms in the elected post. He has become well-known in the legal community for his quiet, unassuming manner and his dry sense of humor.

“There are a lot of people who stay in the criminal justice system too long, and I didn’t want to be one of them,” he said. In retirement, he hopes to spend more time cooking and traveling with his wife; they are planning trips to Southeast Asia and Italy. He will also be able to devote more attention to his 91-year-old mother, who lives in Woodbridge.

The Alexandria Commonwealth’s Attorney’s office has 13 prosecutors who oversee several thousand cases a year, including about 700 felonies. Sengel said he would like to see a bigger focus on white-collar crime, which he says is “becoming much more frequent and much more difficult to prosecute.” To that end, he has pushed to devote more resources to computer forensics to probe financial schemes.

In past years, he has lobbied for more money for DNA testing, both to implicate and help rule out suspects. In 1993, Sengel was involved in one of Virginia’s first exonerations involving DNA, recommending that a 1986 rape verdict be overturned.

But he says he believes he has succeeded in his main goal in running the office: assembling a staff that is supportive of one another.

“With the amount of stress this job brings on, it’s important to have not just colleagues, but friends,” he said.

Sengel will be succeeded by Assistant Commonwealth’s Attorney Bryan Porter, who ran unopposed in the fall. Sengel is “an outstanding attorney, and he’s been a wonderful guy to work for,” Porter said. “He knows a lot about being a good person.” Early on in his career in the office, Porter helped handle a case of a police-involved shooting. He offered to convene a grand jury; Sengel told him no — that it was his job to make those decisions.

One such case occurred in February, when police fatally shot Taft Sellers, a former Marine who was armed. Sengel put out a 30-page report, finding that the officers acted in self-defense. Another such case occurred in 2006, when an off-duty officer working as a security guard killed a teenager in a car driving at him in an IHOP parking lot. He also was not charged, after a three-month review that Sengel described at the time as “one of the most difficult cases I’ve ever had to resolve.” The city paid the teen’s family $1.1 million, and several police policies were ultimately changed.

In May, Sengel’s office charged Arlington Sheriff’s Deputy Craig Patterson with murder in the shooting of Julian Dawkins, 22. Patterson was convicted of voluntary manslaughter.

Several high-profile slayings during Sengel’s tenure have yet to be prosecuted, including those of real estate agent Nancy Dunning in 2003 and transportation planner Ronald Kirby in November. No arrests have been made.

The man implicated in the death of Kevin Shifflett, 8, who was stabbed in April 2000 while playing outside a relative’s home, has been deemed not competent to stand trial and remains in treatment. “My goal has always been to try to do something with that case that protects and keeps the defendant in a secure facility, and so far we’ve been able to accomplish that six months at a time,” Sengel said, referring to the regular court reviews of the suspect’s mental state.

But having prosecuted crimes decades after the fact, he believes that case could one day go to trial, along with the city’s unsolved killings.

Porter said he admires Sengel’s ability “to absorb the anger and frustration” that victims’ families experience and be “a calming influence on people who are really at their worst.”

Sengel said he may have “inherited” some of his touch with people from his father, a Presbyterian minister who died in 2011.

The prosecutor’s legal adversaries say they, too, appreciate his approach. “Mr. Sengel deservedly enjoys a reputation for fairness and integrity, as does his office,” said Joe King, a defense attorney who represented Patterson.

Sengel served on the Virginia Criminal Sentencing Commission and the Virginia Forensic Science Board under then-Gov. Mark R. Warner (D). He serves on the board of the Center for Alexandria’s Children, which works to eliminate child abuse.

“He does what he does for the good of the system,” said Arlington Commonwealth’s Attorney Theo Stamos, who has known Sengel since she began her career as a prosecutor. “He’s not a grandstander.”

In a goodbye message to his staff, Sengel invoked Shakespeare’s King Henry V leading an outnumbered army to battle by declaring that those who do not fight will wish they had.

“Those of you who continue on, never forget the bond this work creates, and the proud band you are privileged to be a part of,” he wrote. “Being able to be a part of it for as long as I have is a gift I will always treasure.”

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