She was a young, spirited and lively woman who wanted to be a physician. A dean 's list honoree for fall 2005 and spring 2006, she was majoring in medical microbiology and immunology at UW-Madison.

She liked to cook, hang out with friends and volunteer for good causes. Engaged to a fellow student, she was looking forward to being married and having children.

Brittany Zimmermann was 21, and earlier this month, she was murdered in her Downtown apartment. Madison police say she was killed by a stranger. And the randomness of that act has shaken many in and outside the Downtown community and raised questions about safety in a fast-growing city.

I think of her every morning when I drive by the blue house where she lived with her fiance. I think of her dreams for her future and how focused and prepared she was to make them real. And I think of her fiance, her family and their immeasurable grief.

The house is on a neat, tree-lined street, a block from where I live. On warmer days, young men from nearby homes leap into that street straining to catch a football. Music and laughter spill out from the houses and condos. Bikers, runners, walkers and pets crisscross the neighborhood, which is close to a bike path, Lake Monona, Capitol Square and State Street.

The normalcy of those acts and this neighborhood makes Zimmermann 's murder surreal. It 's hard to imagine that someone forced open the house 's exterior door, walked in, found her in one of the two apartments in the house and stabbed her to death -- all during the day.

The killer left and, three weeks later, is still free.

Madison police are hard on the case, but their task is daunting. They have to find a murderer with no apparent links to the victim. And until now, they have no motive, no suspects and no witnesses.

That leaves me and many of my Downtown neighbors with this creepy feeling of being watched and feeling unsafe. For many of us, the feeling has intensified because two other recent murders -- of Madison residents Kelly Nolan and Joel Marino -- remain unsolved.

It 's a new feeling for me. I 've lived Downtown for a few years now and never felt particularly threatened or fearful, despite panhandler solicitations and bar-goer brawls. I have great neighbors. But now, I am wary and watchful. I listen for the sharp click of the lock on my front door. I wait until the garage door shuts. I am careful not to walk or bike alone after dark.

These are all common-sense measures that everyone should take at all times. Yet, I 'd be the first to admit that living in welcoming and safe Madison has made me forget things that were second nature when I lived in larger cities.

Madison isn 't becoming worse, but it is certainly becoming bigger. And this growth creates its own safety challenges. People aren 't as likely to know who lives nearby, and strangers can easily slip in and out of communities.

Zimmermann 's death may or may not have anything to do with these changes. But as Madison grows, we have to stay vigilant and make more of an effort to know our neighbors and work together to protect our communities.

It just may save someone 's life.

Ali is an editorial writer and the interactive editor for the State Journal. Contact her at aali@madison.com or 608-252-6163.

Help police If you or anyone you know has information that could help solve this case, please call Madison Area Crime Stoppers at 608-266-6014.