NEWNAN, Ga. — It’s been 12 years since someone shot and killed a teenage boy in Coweta County and the Newnan Police Department is breathing new life into the case.

“This investigation will conclude only when those responsible for the homicide are held accountable and prosecuted to the fullest extent of the law,” said Det. Marcos Gonzales.

That was the last time police believe anyone saw Blake Chappell. He was going to walk to a friend’s house in the Summergrove subdivision but never made it.

In Dec. 2011, police found his body in a nearby creek. The medical examiner says that someone shot and killed the teenager.

Gonzales said the department followed all leads in the case but never made an arrest.

Now, police are adding another detective to the case. The team will re-examine old leads and follow any new ones. Plus, they urging one person to come forward: an anonymous tipster.

“In 2011, we received a letter with an anonymous tip,” said Gonzales. “Several years later, we received a second letter. It is our belief that these letters were written by the same person.”

Gonzales said the writer can remain anonymous, but police want to talk to them to re-examine and verify their information.

You can contact police by calling 770-254-2355. You can reach Crime Stoppers of Greater Atlanta at 404-577-8477. You can also send an e-mail.

WSB-TV’s Courtney Francis contributed to this report.