Authorities believe James C. Kopp, the anti-abortion activist wanted for questioning in the murder of Dr. Barnett A. Slepian, may have fled to Mexico.
Police said they turned their attention toward Mexico after learning that a car owned by a "woman associate" of Kopp's passed over the Mexico border days after the sniper slaying of the physician in his Amherst home.
Investigators believe that Kopp, who is sought as a material witness, may have been in the woman's car when it crossed into Mexico.
And the woman, whose name is being kept secret by police, is expected to come to Buffalo within the next few days to be questioned about Kopp's whereabouts.
"She is going to be questioned, and it is believed that she may have been with Kopp sometime after the murder," one investigator told The Buffalo News Thursday.
"Kopp may be in Mexico. He may have even traveled further into Central America or South America. (Information about) him is being circulated to police down in Mexico."
Paul Moskal, spokesman for the Buffalo FBI office, said he could not comment on the possibility that Kopp is in Mexico. Moskal cautioned that the public and media should not jump to any conclusions about where Kopp may have gone after the Oct. 23 slaying.
But another law enforcement official said the possibility of Kopp hiding out in Mexico is "definitely being explored."
"There is some very proactive investigation work going on down there," the official said. "In some ways, it makes very good sense for him to go down there. Everybody (in law enforcement) expected him to go up into Canada, where he has a lot of contacts."
Even though he has not been called a suspect in the Slepian case, Kopp, 44, has been the subject of a huge manhunt since a few days after a sniper killed Slepian in the kitchen of his East Amherst home.
Authorities confirmed last week that a federal grand jury in Buffalo is already gathering evidence and hearing testimony about Kopp.
Meanwhile, officials of the Hamilton Spectator newspaper in Hamilton, Ont., said they had received another package of anti-abortion literature Thursday, the third such delivery since Slepian's shooting. It included a photocopy of a map that appeared in the newspaper showing the locations of attacks on doctors who perform abortions.
Investigators said they believe all the packages -- there have been seven -- came from the same source. Earlier this month, employees at the newspaper identified Kopp as the person who delivered two of the packages to the newspaper.