While authorities continue the hunt for Vanessa Marcotte's killer, theories are circulating that a serial killer could have targeted her. An Australian news source has speculated openly that the slain jogger's murder appears to be similar to the deaths of at least two other women.

A traveling serial killer to blame?

Vanessa Marcotte was murdered approximately a week after New York woman Karina Vetrano was murdered. Vetrano was attacked by an unknown predator while she was on her daily run -- much like Marcotte -- and that's not the only similarity.

Marcotte was slain in Princeton, but she had only been visiting her mother at the time. The slain Google employee actually resided in New York -- just like Karina Vetrano. Prior to the murder of Karina Vetrano, petite brunette Ally Brueger was killed while jogging, in the state of Michigan.

While these three murders were committed in different states, it certainly wouldn't be out of the ordinary for a serial predator to operate while traveling. The prolific killer Israel Keyes immediately comes to mind when thinking about this topic. Israel Keyes traveled from one end of the United States to the other, claiming numerous victims (many of which have never been discovered). Keyes was ultimately caught after he kidnapped and murdered Alaska woman Samantha Koenig.

Similarities between victims are troubling

All three women in the cases mentioned above are strikingly similar in appearance. All three victims were young, petite, athletic and brunette with feminine, conventionally attractive features. All three female victims were avid joggers, who had set daily routines for running. Furthermore, all three victims appeared to be involved in similar industries and interests.

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Ally Brueger was a writer. Karina Vetrano was a blogger. Vanessa Marcotte was a Google,account manager. All three victims were slain and left in the close vicinity of their homes -- or in Marcotte's case, close to her mother's residence.

With all the similarities between these three cases, it would seem foolish for detectives not to investigate the possibility of a serial killer.