(CNN) -- Police arrested a former Creighton University medical resident Monday for two double homicides over five years, both sets of victims were connected to the pathology department at the Nebraska school.
Anthony Joseph Garcia, 40, was arrested during a traffic stop in Illinois, Omaha Police Chief Todd Schmaderer said. Officers were making preparations to arrest him Tuesday, but the Indiana resident "became mobile" and police felt they needed to arrest him right away, he said.
Garcia was arrested on four counts of first-degree murder in the May deaths of Roger and Mary Brumback, both 65, and the March 2008 deaths of 11-year-old Thomas Hunter and his family's housekeeper, Shirlee Sherman.
All lived in Omaha.
Roger Brumback was a professor in the pathology and neurology departments at Creighton and announced his retirement shortly before he was killed.
Thomas Hunter's father, Dr. William Hunter, is a faculty member in Creighton's 12-person pathology department. The boy's mother, Dr. Claire Hunter, is an associate professor in Creighton's cardiology division.
Garcia was a resident who worked in the pathology lab from July 2000 until June 2001, when the Brumbacks and William Hunter fired him, the university said.
Neither police nor the university said why Garcia was terminated, but CNN affiliate KETV said it was because of "erratic behavior."
An Omaha task force had been monitoring Garcia "for some time," Schmaderer said. He was pulled over for suspected alcohol impairment and was found with a .45 handgun.
Authorities believe Garcia acted alone, Schmaderer said.
It's not clear where Garcia was working at the time of his arrest.
"Creighton University and particularly the School of Medicine and Department of Pathology are grateful for the work of the Omaha Police Department and the special task force in these investigations," the school said in a statement late Monday.
CNN's Dave Stewart contributed to this report.