County police on April 20 posted a request for tips from the public to help catch an armed suspect in an attempted rape near Arlington Mill.

The next day, using a description assembled from witnesses, surveillance units spotted Jermaine Johnson fleeing a residence, and he was arrested and charged.

That’s quick crime-solving. Other local cases end up tougher however, and drag on for decades.

You can see a list of Arlington’s 21 languishing cold cases on the police website. The details of cases going back to 1970 – victim, crime, location, suspect descriptions – are inconsistent and frustratingly vague.

But each represents life-altering heartbreak for victims and families. Consider:

• Paul Zeller, a 24-year-old Iraq war veteran, was murdered on June 30, 2006, while walking near Pentagon Row shopping center. He was shot on the street after leaving a store. Witnesses heard shots and called 911.

• Vu Huynh was shot to death March 23, 1997, in the parking lot of Hi Cue Billiards on S. George Mason Drive. The suspect was an Asian male dressed in black, perhaps a member of the Laos Bloods or Dragon Fly gang.

• Dorothy Townsend was found asphyxiated on Jan. 21, 1975, at the 2500 block of Jefferson Davis Highway. Police were notified when she did not return to her shift as a concessions stand clerk. The robbery suspect was later described as a black male, 20-25 years old.

For some cases, I’ve gathered additional information from news clips and police.

Just after midnight on June 11, 1992, at the Roy Rogers restaurant at Lee Highway and N. George Mason Drive (now Capital One Bank), an unidentified person entered. He stabbed Sanford Swift, a 42-month employee, then made off with money from the register.

Swift’s body was discovered next morning by co-workers. No signs of forced entry, Arlington Det. Greg Brewer told The Washington Post. Years later, Roy Rogers employees still discuss their shock, I was told recently by one of them, Norman Leppert, who sent police suggestions for witnesses in the neighborhood.

Another for which I can add details involved State Department security specialist John Herse. In the early 1970s, he helped tracking down fugitives such as LSD advocate Timothy Leary and financier Robert Vesco.

On Aug. 14, 1974, Herse was walking with his wife from Tom Sarris’s Orleans House Restaurant in Rosslyn when three black males approached them from behind and pushed Herse to the ground. One suspect shot him dead. Robbery was not the likely motive, given the $500 left in Herse’s wallet.

In 2010, a retired FBI profile was mulling the case, according to documents published on Wikileaks. A private intelligence company had interviewed Mrs. Herse. “The wife believes the shooter fired with a degree of discipline (two hands on the gun),” the documents noted. She later suspected a black radical author she saw on television who resembled one assailant.

Arlington police lack a separate budget for cold cases, according to spokeswoman Ashley Savage. The work falls within the Homicide/Robbery Unit and the budget of its Criminal Investigations Section.

The cold case list has remained steady in recent years, Savage added. Only one — the 1971 shooting death of Hugh Howard in his parents’ home on South Eads St., was recently removed after the suspect died.

If you have helpful info, call the ACPD Tip Line at 703-228-4242.

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John McNair, tour guide at the new Civil War visitors center at Fort C.F. Smith, was kind enough on April 21 to stay open past the weekend 2 p.m. closing.

That allowed the tardy a quick peek at the interactive soldier roster, the tintype portraits, recovered shell casings, clay pipes and belt buckles from fort built in 1863 among the string across Arlington that protected Washington from southern threats.

Also on display at the hike-able park just off Spout Run: recreated union uniforms and period tents, plus a shelf of the Time-Life Books Civil War series and an 1895 multi-volume collection of Civil War correspondence.