"We have worked hard at this, we wanted to clear the president of the United States, but it hasn't happened like that," Arpaio said.
KNXV-TV, Phoenix, reported county investigator Mike Zullo said he believes someone had tampered with Obama's birth document in Honolulu and the Maricopa County investigative team can prove it has been manipulated.
Zullo said the investigation brings into question the citizenship of anyone with a birth certificate from Hawaii.
"It's time for this charade to stop," Zullo said, adding he wants the U.S. Congress to investigate as well.
Arpaio said he believes Obama's birth certificate, released last year, is a "computer-generated forgery," the TV station said.
The sheriff, who said he took up the investigation at the behest of 250 state residents, said he's not suggesting Obama was involved or challenging his legal status, but he believes a crime occurred.
In an attempt to lay to rest allegations that Obama was not born in Hawaii, the White House last year released the president's certificate of live birth.