Female joggers attacked across U.S.: Single assailant or random acts?

Is it open season on female runners? It seems like a nationwide epidemic.

In New York, there's the tragic unsolved case of Karina Vetrano, murdered while running through a Queens park. Police are still actively looking for her killer. Now there's another sad story of a woman attacked while out for a jog in Michigan.

One by one, joggers killed or kidnapped in the middle of a run. Haunting video shows Karina Vetrano jogging in a park in Queens just minutes before she was murdered on a remote trail.

Vetrano's murder has New York City on edge. The NYPD's chief of detectives Robert Boyce is working tirelessly to solve the killing.

The most recent mystery across the U.S. on the other coast, in Redding, California.

UPDATE Nov. 24, 2016: Missing Shasta County mom Sherri Papini found alive - KTXL

Sherri Papini was last seen jogging in her neighborhood near the foothills of Mount Shasta. Sherri's distraught husband Keith speaking to our Redding affiliate KRCR.

Sherri vanished into thin air in broad daylight. Her family believes she was kidnapped. Keith found Sherri's cellphone down the street, and her pink jogging jacket was spotted nearby.

UPDATE Nov. 24, 2016: Missing Shasta County mom Sherri Papini found alive - KTXL

Just months ago, in Rose Township, Michigan, outside Detroit, another mystery deep in the woods. An unidentified man found a female runner shot dead in his yard, murdered by an unknown assailant. It was Alexandra "Ally" Brueger, a nurse. She was on her daily 10-mile run in a wooded area when she was gunned down.

Just like Karina Vetrano in New York, who put up a fight, Ally's mother says she put up a brave fight against her killer. Michigan State Police were called in to investigate Ally's murder. The killer is still on the loose, leaving the small town in fear.

In Princeton, Massachusetts, west of Boston, cops have checked out almost a thousand tips in the killing of Vanessa Marcotte. Vanessa lived in New York City and worked for Google. She was visiting her mom and went out for a Sunday afternoon run. She never returned. Police found her body a half-mile from her mother's home, naked and burned.

Is there one assailant travelling from state to state, picking off women jogging? Or are these simply random acts of evil? No one seems to know.

But there's hope that Sherri Papini could still be alive.