In a fledgling crime career cut short by ineptitude and arrest, Arvel Crawford left three men dead on the ground in a pair of unrelated shootings before his 20th birthday, according to D.C. homicide detectives. Evidence suggests that he had a beef with only one of the deceased and that the others — including his father, also a felon — were simply victims of the young man’s poor marksmanship.

Crawford is serving an 18-year prison sentence for one of the killings, which occurred during a botched attempt to rob a suspected drug dealer in late 2009. Among his five partners in the failed stickup were his dad, Arvel Alston, and a uniformed, on-duty D.C. police officer who acted as a lookout in a marked cruiser.

Almost everything that could go wrong that night did, and Crawford, while trying to shoot the suspected dealer, accidentally put a bullet in his father. “Get up, Dad! Get up!” the son yelled, to no avail. Soon afterward, Crawford was in handcuffs.

It turns out that Alston wasn’t the only casualty of careless gunfire by his son, police said. They announced Thursday that Crawford has been charged in a 2008 double homicide in which he allegedly planned to kill one man. The other victim, a 61-year-old homeless crack user and petty thief, just happened to be loitering nearby when he was felled by a .45-caliber slug, apparently a stray.

His name was Nolan Cooper, and he was collateral damage — a stranger to Crawford and to the target of the shooting, 18-year-old JohnQuan Wright.

“That’s pretty much all it was,” a police homicide supervisor said Friday. “Coop­er was a bystander, quote-unquote. Nothing more complicated than that.”

Yet murder is seldom simple in the District, where one killing frequently begets another in a continuum of retaliatory street violence. It took detectives more than three years to extract enough information from witnesses — not all of whom saw the shooting — to warrant charging Crawford in the deaths of Wright and Cooper.

Crawford’s version of the killings isn’t known. He has neither appeared in court yet nor entered a plea. But it is no surprise that the lifeless bodies of Wright and Cooper weren’t the only corpses that police have connected to the case.

It happens like this a lot:

In the wee minutes of June 7, 2008, two months before Wright and Cooper died, a young man named Brandon Pollard was found shot to death in a tumbledown neighborhood a half-mile northwest of Union Station. Pollard, 19, was one of JohnQuan Wright’s cousins, police said. Naturally, Wright was aggrieved.

Vengeance apparently was meted out six weeks later a few blocks away, where 18-year-old Darron Williams was gunned down on the night of July 24. Williams was one of Crawford’s cousins, police said. Witnesses have since told detectives that Wright bragged of killing Williams and that Crawford, then 17, heard about the boasts.

About 10 o’clock on the sun-splashed morning of Aug. 14, Wright was standing on a sidewalk in the abandoned, dilapidated Temple Courts public-housing complex, a short walk from the earlier shooting scenes. A black sport-utility vehicle rolled up. A man got out, pointing a .45-caliber pistol at Wright, whose back was turned.

The hapless Nolan Cooper, who had spent most of that summer behind bars, was a few steps from Wright as the gunman approached. A junkie and chronic shoplifter with a decades-long arrest record for minor crimes, Cooper had been released from the D.C. jail that morning. Temple Courts was where he sometimes went to buy crack.

“Wrong place, wrong time,” the homicide supervisor said.

The assailant squeezed off at least three shots — the spent shells were found on the pavement — and down went Wright, down went Cooper. The gunman climbed back into the SUV and sped off. Police later recovered the .45-caliber semiautomatic a few miles away, wrapped in a T-shirt and buried in a tree box.

At Temple Courts, detectives immediately noted the vast age gulf between the two dead men. Wright, 18, perfectly fit the local homicide demographic. But not the other fellow: At 61, and with no record of serious violence, Cooper seemed far too old and dope-worn to be mixed up in urban combat.

An innocent victim?

“Looks it,” a detective said that day. “Bad aim, maybe.”

It wouldn’t be the last time, police allege.

As the Wright-Cooper case languished unsolved, detectives said, Crawford moved on to other endeavors, culminating in a woefully bungled robbery attempt on the chilly evening of Dec. 1, 2009. The six men in the stickup crew intended to rob a suspected dealer in his drug-stash apartment in Southeast Washington, then abduct him, drive him to his home in Prince George’s County and rob him again there.

That was the plan, at least.

It went straight downhill as soon as the victim put up a fight in the parking lot outside the suspected stash pad, at the Southern Hills Apartments in Washington Highlands. Crawford pulled out a pistol and fired, police said. The bullet missed the intended victim and struck Crawford’s father, 40-year-old Arvel Alston, who was seated at the wheel of the victim’s Infiniti, ready to drive him to Prince George’s.

Alston staggered out of the car, blood spreading across his torso.

“What the [expletive] you doing?” he groaned at his son, before collapsing.

Alston, a convicted killer, was on parole after a 17-year prison stretch that began when Crawford was 6 months old. As a free man, he had met his adult son for the first time in 2007, and here they were, two years later, buddies in crime.

“Get up, Dad!” But he never did.

Crawford and the others — including Officer Reginald Jones, then 40 and a six-year member of the D.C. police force who was in dire financial distress — took off in a hurry. Jones’s role in the robbery was to sit in a marked car and shoo away anyone who might become a witness. Like the rest, he was quickly arrested. He received a 15-year prison term.

Crawford pleaded guilty to second-degree murder in his father’s death and was sentenced to nearly two decades behind bars.

He turned 21 last month.