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(UWIRE) -- After six hours of searching Hickory Hill Park Wednesday with an infrared-equipped plane, police were unable to find missing University of Iowa Professor Arthur Miller.
Police believe Miller was in the park after his red BMW was found in a parking lot at Hickory Hill Park.
Miller, who police say may be dead, is thought to have a rifle with him.
The UI faculty member was charged on August 8 with four counts of accepting a bribe. More accusers have contacted authorities about Miller, said Charles Green, the assistant vice president for the UI police.
Police followed an initial sweep of the park Wednesday with nighttime state patrol plane flyovers employing infrared cameras.
Thursday's search, which began at 7 a.m., focused on finding a body, Kelsay said. Cadaver dogs were used.
"We're transitioning back to search mode to find a body and rifle as opposed to an ambush," Kelsay said. "But until we find him, it is a continued public safety risk."
While police are carefully searching the 185-acre park, they are still monitoring Miller's bank accounts for signs he has fled.
Police believed Miller was in the park after his red BMW was found in a nearby parking lot.
Police used his cell phone, which was left in the car, to triangulate his general area.
Miller's was last seen Tuesday morning and his wife reported him missing around 7 a.m. Wednesday. The last call on his cell phone was placed at 9:30 a.m. that day.
Miller's wife also reported that the 66-year-old left a note, which Kelsay said was "apologetic" and "cryptic enough that it causes concern he may be out to harm himself."
Miller purchased a rifle on June 13, Kelsay said.
Miller was denied a weapons permit filed June 24 for a handgun, Johnson County Sheriff Lonny Pulkrabek said. Pulkrabek had denied Miller the permit because UI officials said he was under investigation in a bribery case.
Police also searched Miller's office and other university locations. Jessup Hall was briefly locked down, UI police said.
In addition, all Iowa City School District schools were locked down Wednesday around 3 p.m. Officials lifted the lockdown a half hour later, Associate Superintendent Jim Behle said.
Police are urging non-emergency personnel to stay out of the park.
The day of searches and lockdowns capped a drama that began in May, when four female University of Iowa students accused Miller of wanting to exchange sexual favors for higher grades in his class. He has since been placed on paid administrative leave.
In one complaint, a female student told police that during a meeting with Miller, he said she wasn't doing well in regard to her grade. He then allegedly told her she would "have to do something for him." She said Miller then grabbed and sucked on her breast.
The student later allegedly received an e-mail from Miller, congratulating her on getting an "A+" grade and offering assistance with getting into law school.
In another instance, a female student said Miller offered to give her an "A" grade if she let him fondle and lick her breasts. In an e-mail later, he wrote that "a lasting memory of a lovely Monet cannot be formed in 20 seconds," according to reports.
A third female student told police that Miller once asked her to take off her top in order to improve her grade.
He allegedly asked a fourth female student to take off her top, telling her that women in New Orleans "do it all the time just for beads" and that her grade was "on the line," police reported.
Search warrants in the case show that police now have access to nearly 50 sets of e-mail exchanges among Miller and more than 15 students, UI officials, and other unknown people.
Linda Maxson, the dean of the UI College of Liberal Arts and Sciences, said Miller would not be permitted to return to campus in the fall.
"With charges like this, we don't permit him in the classroom," she said.
A secretary for UI spokesman Steve Parrott said all calls related to the case were being routed to the university's general legal counsel, Marc Mills.
Mills did not return calls seeking comment.
UI President Sally Mason announced last week that all university faculty will receive sexual-harassment training. Such behavior "will not be tolerated," she said in a letter to faculty and staff.
"It is profoundly damaging to the students and to the educational process," Mason wrote. "I applaud the courage of the student victims in coming forward to report this conduct to the Office of Equal Opportunity and Diversity and to the UI Police Department."
In a news release early last week, UI officials said they are conducting an investigation separate from the criminal one.