Running scared: Three young female joggers murdered in nine days. Could they be related?

Karina Vetrano, 30, was killed in New York City on August 2 after going for a run. Photo / Instagram

Contrary to urban legend, it's extremely rare in America for a woman to be murdered while jogging; according to crime statistics, she is much more likely to fall victim to a road accident.

So when three young female runners are slain in America's northeast in the space of just nine days people start looking for connections, for evidence of a serial killer at work.

There are unsettling parallels between the murders of registered nurse and writer Alexandra "Ally" Brueger, 31, in Michigan on July 30; caterer and blogger Karina Vetrano, 30, in New York City on August 2; and Google employee Vanessa Marcotte in Massachusetts on August 7.

This undated driver license photo released by the Worcester County District Attorney's Office shows Vanessa Marcotte, of New York, whose body was found on August 7.

Although they occurred in different states, the women were all attractive, petite brunettes (in some photographs, Vetrano and Marcotte could be mistaken for sisters) of a similar age who were attacked while on their daily run.

Marcotte and Vetrano share a New York connection; Marcotte was murdered while visiting her mother in the tiny Massachusetts town of Princeton but was based in the Big Apple.

She worked at Google's Chelsea office, which is located just 30 minutes from the New York borough of Queens, where Vetrano was murdered less than a kilometre from her family home.

Brueger and Marcotte were slain in small towns where violent crimes are rare compared to the rest of America; Brueger's murder was the first in Rose Township, Michigan in 20 years while Marcotte's death was Princeton's first homicide in nearly three decades.

Registered nurse and aspiring writer Ally Brueger, 31, was shot in the back on July 30.

"We haven't ruled anything out in regards to the New York homicide. There are similarities," Worcester County, Massachusetts District Attorney Joseph Early, Jr told reporters on August 9. "We have to let all the evidence, all the facts play out."

Early was not asked about a possible connection to Brueger's case at the time.

Since the weekend, the nurse and aspiring writer's picture has started appearing alongside those of Vetrano and Marcotte in the US press as speculation grows that all three may have been targeted by a serial or copycat killer.

However, the crime scenes are also sufficiently different to support the possibility that three homicidal maniacs, all of whom have so far managed to elude the national DNA database, attacked female joggers in different states within nine days of each other.

Brueger was shot four times from behind as she went on her daily 16km run along Fish Lake Rd in Rose Township, an isolated dirt track.

Michigan State Police said residents at a handful of nearby homes reported hearing several gunshots but ignored them because the area was popular with hunters.

One curious neighbour did step outside to find a woman bleeding on his front lawn. He called police and gave the woman, later identified as Brueger, CPR until the paramedics arrived, according to Click on Detroit.

The good Samaritan told police he did not catch sight of the shooter.

Investigators found fresh tire marks on the gravel road, but they don't reveal if the killer was in car or ran off into the woods.

Michigan State Police said there was a strong possibility Brueger knew her assailant and have asked the public to help trace a "white or light-coloured four-door vehicle" seen in the area at the time.

Karina Vetrano usually jogged with her father, a retired firefighter but ran alone the night she was murdered. Photo / Instagram

Vetrano was beaten, raped and murdered as she went for her evening jog through Spring Creek Park in Queens. A post mortem examination indicated she had been strangled.

The New York Times said Vetrano had a master's degree in speech pathology and worked for several years at a club in Queens and was previously employed at a restaurant and wine bar. She also wrote a prolific blog in which she discussed love, sex, her own funeral - and murder.

Marcotte's body was found in the woods near her mother's Princeton home hours after she failed to return from a lunchtime run.

Investigators said she had been raped, strangled and set alight. Police suspect the killer knew he left DNA on her body and tried to eliminate it with fire.

The murders have prompted community women's running groups in New York, Princeton and Rose Township to start their own safety campaigns.