The Associated Press

COLUMBUS - Investigators haven't been contacted by anyone claiming to be the Interstate 270 highway gunman, despite repeated requests by authorities.

And they say they are not aware of any copycat cases.

Franklin County Sheriff's Chief Deputy Steve Martin said Wednesday that about 1,600 tips have been received on 15 shootings along the southern stretch of I-270, including one that killed a woman. The tips include reports of suspicious cars and activities, he said.

In comparison, investigators in the Washington, D.C., sniper case received 50,000 to 70,000 tips, and authorities in West Virginia have received 2,400 tips on three unsolved fatal shootings in August outside convenience stores.

In his daily briefings, Martin routinely asks the gunman to call a tip line or write the sheriff's office at a post office box number.

So far, bullet tests show six of the shootings came from the same gun, he said.