A college student vanished in June after a night of barhopping; her body was found in the woods days later. In January, a 31-year-old man was stabbed to death with a paring knife in his home near the University of Wisconsin-Madison in what police called an apparently random act.
And a few blocks away, police on Wednesday found the body of UW-Madison junior Brittany Sue Zimmermann, 21, from Marshfield in the apartment she shared with a boyfriend. Police aren't saying how she died, only that she was the victim of a homicide.
They say it's too early to tell whether the three cases are linked. That's little comfort to wary residents.
"I'm extra scared because of the little bit of information that's been released," said Christian Caflisch, 23, a recent UW-Madison graduate who lives less than a block from Zimmermann's apartment. "They are basically telling us, 'A killer is out there. Be safe.' It's a bit disconcerting."
Madison police on Thursday continued looking for evidence in the neighborhood - a mix of large old houses packed with students and new condominiums popular with upscale residents. Several officers remained in front of Zimmermann's green apartment, interviewing neighbors and passers-by.
CBS affiliate WISC-TV reports an incident which took place at about the same time her body was found is also being investigated. Police are looking into a report of an intruder who entered a house shared by several students through an unlocked door. The suspect left upon discovering someone was inside.
Lori Berquam, UW-Madison dean of students, called Zimmermann's death "extremely unsettling." She described Zimmermann, who studied medical microbiology and immunology, as a dedicated student and employee of the registrar's office.
"She was a good-natured, friendly individual who really took pride in being a student here. That's why it's so hard to make sense of this," she said. "There's been a great deal of concern and a whole lot of emotion about the horrific nature of this. ...This happened in her home. In the middle of the day."
The university planned a vigil for her on Sunday and described her as a driven student who had a bright future in the field of public health. She planned to attend medical or graduate school after her anticipated graduation next year.
The Dane County coroner's office said an autopsy Thursday confirmed her death was a homicide caused by "a complexity of traumatic injuries." The office said it would not elaborate, citing the ongoing investigation.
Her boyfriend, who discovered the body Wednesday afternoon, was ruled out as a suspect on Thursday. Police said he was cooperating with detectives.
Madison police spokesman Joel DeSpain noted several similarities between the slaying of Zimmermann and the January killing of Joel Marino, who was found dead outside his home with stab wounds.
Police believe he died trying to crawl to a hospital. Both were killed in their homes in the middle of the day. Both were described as good people unlikely to be targeted.
"There's some similarities, but we don't have anything to suggest definitively at this point that it's the same person or persons," DeSpain said. "That's one avenue among the many that will be looked at as both cases are analyzed."
In the Marino case, police released a sketch of a man witnesses saw in the area. He is a white man in his 20s, between 5 feet 10 and 6 feet 2 with a thin build, wearing a knit cap with a UW logo.
The state crime lab has linked DNA from the paring knife used to DNA found on a backpack and winter cap police believe the assailant discarded as he fled the scene.
The June slaying of Kelly Nolan appeared to follow a different pattern, DeSpain said, but police are not ruling out a link. The UW-Whitewater student was living in Madison when she disappeared after a night of drinking with friends. Her decomposing body was found days later in a rural area about 10 miles south of the city of about 223,000.
Police do not have a suspect, DeSpain said.
Despite the high-profile slayings, Madison remains a safe city compared with others its size. Violent crime dropped about 15 percent in 2007 from the year before, according to FBI statistics.
"Violent crime overall has been down quite a bit, but that's not much comfort to the people involved in this latest act," said George Twigg, a spokesman for Mayor Dave Cieslewicz.
Residents said they are frustrated that the killer or killers have so far eluded police and about what they call a lack of official information. They said they were locking their doors, looking for suspicious individuals and avoiding walking alone at night.
Cheyanne Cyr, 20, who walked her dog in the neighborhood Thursday morning, said she was taking precautions but worried someone could still break into her house.
"I think it's pretty scary. I was really shocked when I heard about it last night," said Cyr, a student at nearby Edgewood College. "I would really hope they would find the person who did it. I mean, are the Madison police doing their jobs?"
Caflisch said he spent last night at the nearby home of his girlfriend, also a student, at her request. As he spoke, a police siren sounded in the distance.
"Now every siren you hear, you think the worst," he said. "It's very scary."