Ayres' body was found with multiple stab wounds in the soccer field in Southampton, Burlington County on Monday morning.
The discovery was made in an athletic recreation area where Buddtown Road and Route 206 meet in Southampton Township.
It was around 10:30 a.m. when some public works employees went to a wooded area to retrieve some topsoil and found her body instead.
Police on Tuesday arrested Stephen Headley, 28, of Florence, N.J., on murder charges.
Investigators said the murder is believed to have occurred early Monday morning, but they were investigating the motive.
That night Headley asked his grandmother, a resident of Medford Township, to drive him to his mother's house in Pemberton Township because he wanted to meet with the two of them.
During that meeting with his mother and grandmother, he fled the house and ran into the road, where he was hit by a pickup truck.
Headley was airlifted to Capital Health System, Fuld Campus in Trenton where he is being treated for a fractured back, two fractured ankles and multiple fractured ribs.
He will have a first appearance in Burlington County Superior Court upon his release from the hospital. Bail was set at $750,000 with no 10 percent option.
Ayres, a Deptford High School graduate, was the softball rookie of the year at Fordham University in New York City.
Ayres had left the university after the 2008 spring season and was registered for a full slate of classes this fall as a sociology major at Rutgers-Camden, according to officials there.