KEY EVENTS

• April 2: UW-Madison student Brittany Zimmermann, 21, is killed and found at her West Doty Street apartment. Police release little information about the investigation, but one focus is on transient men who panhandle in the area. Authorities never say a 911 call was made from her cell phone around the time of the slaying.

• May 1: The weekly newspaper Isthmus reports there was a 911 call from Zimmermann's cell phone but the dispatcher who took the call believed it was a mistake and never sent police to check on her.

• May 1: In response to the disclosure, Dane County 911 Center director Joseph Norwick admits the dispatcher erred by not calling the number back, something he says she was required to do under the center's protocols. He says the dispatcher heard nothing on the call and hung up, but Police Chief Noble Wray says there was enough evidence on the call to send police to the scene. Norwick says an internal investigation is ongoing but the dispatcher has not been disciplined and remained on the job. Norwick also maintains tracking the location of cell phone calls is difficult, while Wray says the 911 center has sufficient technology to track cellular calls.

• Friday: Contrary to what the Norwick said the day before, he now acknowledges that the dispatcher who took the Zimmermann call was transferred shortly after April 2.

• Sunday: The State Journal reports that a 2004 strategic plan for the 911 center, conducted by consultants, warned of "possible liability and the potential for a catastrophic event" if county officials didn't take steps to increase staffing, change procedures and enhance oversight. County officials say they have already acted on many of the recommendations contained in the report.

• Monday: A manager who worked on the plan, Robert Kaelin of Seattle-based MTG Management Consultants, says his firm recommended in 2004 that the staffing increases at the 911 center be made "right away." County officials say staffing changes were implemented as part of a five-year plan and that there is no current staffing shortage at the center. To date, the staff increases recommended in the plan have not been fully implemented.

• Tuesday: Authorities reveal for the first time that shortly after the call from Zimmermann's cell phone, the 911 center erroneously told Madison police it had called the number back and contacted two unidentified males. Almost two weeks later, the 911 center realized the number the dispatcher had called back was not Zimmermann's. In the meantime, police had been pursuing contacts with the two males as part of their investigation. County Executive Kathleen Falk's chief of staff Topf Wells acknowledged that, contrary to what Falk's office had said, the dispatcher who handled the Zimmermann call had asked for a transfer from the 911 center in March. The transfer was completed after April 2. Falk also says that contrary to what Norwick said, it is not known who ended the call.

• Wednesday: WISC-TV reports that a union representative for county dispatchers says the dispatcher who handled the Zimmermann call contends she did nothing wrong and it is the 911 center's policy to call back disconnected calls only if the dispatcher has time. The representative, Laurie Lane, also says she has heard the call and it is about 90 seconds long and that the only thing that can be heard are faint rustling sounds. She also says the dispatcher did not hang up on the call.