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Could the roommate who leaves her dirty underwear on the floor also be a murderer? Just ask the members of the “I often wanna kill my roommate(s)!” Facebook group. Or the individuals who have “kill my roommate” checked on 43 Things, a website that lets you publicly declare and share stories about your personal goals. There’s even an amusing video tutorial on MySpace that offers suggestions on how to accomplish such a task. But homicidal intentions are sometimes no joke—your roommate’s passive-aggressive Post-it Notes could foreshadow a murder trial that you won’t be able to attend.

We all know that we are more likely to be killed by someone we know—someone intertwined in our daily existence. The odds a victim of a solved murder was acquainted with the perpetrator are 1 in 1.28 (78%). What springs to mind are jealous spouses, crazy parents, or possessive boyfriends. Rarely do we think roommate = lethal threat. But several high-profile homicide cases are suddenly making us think twice about sharing space with strangers.

One place you are very likely to be stuck with a roommate is in a nursing home. In September 2009, a 98-year-old nursing-home resident, Laura Lundquist, became the oldest homicide defendant in Massachusetts state history. She was charged with second-degree murder in the death of her 100-year-old roommate, Elizabeth Barrow. Lundquist allegedly strangled Barrow with a plastic shopping bag after complaining that her roommate was taking up too much space. Though nursing-home caretakers insisted the two roommates were like sisters, before her murder Barrow confided that Lundquist, who is said to suffer from dementia, was making her life “a living hell.”

The title of “most chilling roommate homicide” goes to the case of 21-year-old Meredith Kercher, a British exchange student studying abroad in Italy. Kercher was found half-naked with her throat cut, and investigators believe her November 2007 death resulted from a forced group sex game gone wrong. Three suspects were convicted—most notably Kercher’s American roommate Amanda Knox, a former University of Washington language student, who was 20 years old at the time of the murder.

Each year, hundreds of thousands of college students are assigned to rooms with total strangers. Most of the time, these match-ups are successful, or at least tolerable. But there can be tragic outcomes, as occurred in a Harvard University dormitory in May 1995. Early one morning, Sinedu Tadesse, a troubled 20-year-old pre-med student, stabbed her roommate, 20-year-old Trang Phuong Ho, before hanging herself in the bathroom. Investigators counted 45 stab wounds on Ho, including 11 in the head, chest, and neck. Over a decade later, the motive for Tadesse’s actions is still unclear. Both women were described as quiet and hard-working—and both had applied for a new roommate.

More recently, a Mississippi jury sentenced 29-year-old Bobby Batiste to death for the May, 2008, killing of his roommate, 28-year-old Andreas Galanis. Batiste beat the victim with a rim adjuster when Galanis confronted him about thousands of dollars in missing money.

So the next time you post an ad for someone to share your place, you might want to least check and see if their name appears on the “I often wanna kill my roommate(s)!” Facebook page—or for that matter, among the “Most Wanted” postings at your local precinct.