CLOVIS, N.M. (AP) _ A New Mexico dentist, serving a life sentence in prison for killing a Clovis woman, is a ``person of interest'' in four unsolved Oklahoma homicides, a spokeswoman for the Oklahoma State Bureau of Investigation said. Agents are investigating whether James Smith of Clovis is connected to the deaths of four women around Lawton, spokeswoman Jessica Brown said Saturday. She said he isn't the only person under investigation.

The unsolved killings span from 1999 to 2002. Investigators said bodies of the women, all known to have worked as prostitutes, were found nude near rural county roads in various stages of decomposition.

``We have looked at him (Smith) and are in the process of doing that. The book is not closed on him,'' Brown said.

The 38-year-old Smith's plea came about a year after the December 2005 slaying of Laura McNaughton, 30, a single mother and waitress who was sexually assaulted, strangled and beaten. Hunters discovered her naked body in a rural Curry County ditch.

Smith entered an Alford plea last December to charges of first-degree murder, kidnapping, attempted sexual penetration and tampering with evidence in McNaughton's death. He had faced the death penalty if the case went to trial.

In an Alford plea, a defendant doesn't admit guilt but acknowledges that sufficient evidence exists to convict.

The plea bargain put Smith behind bars for at least 57 years.

Brown declined to discuss whether Smith might have had ties to Oklahoma or a timeline that would place him there. Court records indicate Smith was a student at the University of Oklahoma but the dates he attended weren't listed.

Brown said it's routine for officials to look at ``other people that have been arrested for similar crimes,'' when investigating unsolved homicides.

Officials wouldn't say if a sealed search warrant in the Smith case could be connected to the Oklahoma cases.

District Attorney Matt Chandler said FBI agents served the warrant in November with help from Clovis-area law enforcement agencies. He declined comment on what police were looking for, what was found at the home and what prompted the search.

Brown wouldn't discuss the Clovis warrant but said it is customary to request FBI assistance in investigations that cross state lines. She said Oklahoma investigators, to her knowledge, haven't interviewed Smith.

The Oklahoma cases involve the deaths of:

_Jane Chafton, 29, whose body was discovered Aug. 13, 1999, near Velma, Okla., in a remote area of Stephens County. She had been missing four days.

_Cassandra Ramsey, 25, whose skeletal remains were found five months after her disappearance on March 22, 2000, near a bridge along a rural road in Jefferson County.

_Mandy Raite, 25, who disappeared from Lawton on June 15, 2000. Her body was discovered two days later in a rural area of Comanche County.

_Janice Buono, 29, whose body was discovered Feb. 23, 2002, in Comanche County more than two months after she was last seen.

Brown said investigators are also examining the death of a fifth woman with similarities to the others but haven't determined any connection.