The shooting victim was able to run across the street to the main Durham library for help.
"He had blood all over his shirt. He said 'I'm in trouble. I've been hurt. I've been shot,'" witness Darius Little recalled.
The library staff immediately called for help.
"They administered first aid until the EMT staff got there," said Skip Auld with the Durham library. "The staff is trained to deal with all kinds of situations."
When officers arrived, they found the man lying on the floor inside the library with a gunshot wound in his back.
He was later listed in critical condition at Duke Hospitals.
Surveillance footage shows the man who may be the alleged shooter was riding a bicycle. He left on the bike right after it happened.
A nearby homeless shelter says it's complained to police about the intersection where the shooting took place. It fears it's become a haven for drug trafficking and now a shooting.
Anyone with information is asked to call District Five Substation Investigator A.C. Rogers at (919) 560-4935, ext.29416 or CrimeStoppers at 683-1200. CrimeStoppers pays cash rewards for information leading to arrests in felony cases and callers never have to identify themselves.