The union that represents the former Dane County 911 employee who answered the call from slain UW-Madison student Brittany Zimmermann's cell phone is challenging her three-day suspension.

Larry Rodenstein, a spokesman for AFSCME Local 720, which represents county 911 employees, said the union filed a grievance alleging the county did not have just cause to suspend Rita Gahagan, a 20-year veteran of the 911 center who violated center policy after not hearing a scream on the April 2 call.

After the Zimmermann call ended, Gahagan received a second call from a land line, which was an immediate hang up. She called that number back and was told the call was a mistake. She didn't return the Zimmermann call, a violation of center policy.

Later, other center staff apparently misunderstood the recording system and connected the two calls, sending Madison police after wrong suspects for two weeks before they learned about the error on April 15.

No other 911 employees have been disciplined for errors related to the Zimmermann incident.

Dane County officials didn't discuss the mishandled call until it was disclosed in a newspaper report. They later asserted they could not release certain information related to an internal investigation because of the ongoing police and personnel investigations. Last month, a Dane County judge ordered the county to release the withheld documents, including an e-mail in which Gahagan criticized the equipment and technology at the center.

County officials have said equipment was not a factor in the Zimmermann call and Gahagan did not raise the issue during three subsequent interviews with her supervisor.

Gahagan's suspension was issued in a Dec. 22 memo from interim 911 director Kathy Krusiec, who quoted operations manager Rich McVicar's conclusion that "Gahagan's failure to call back the first call appears to be due to an unintentional oversight likely due to her quickly moving on to handle subsequent calls."

In the disciplinary letter, Krusiec also mentions two incidents in 2007 in which Gahagan was coached for violating center policy.

Before the Zimmermann incident, Gahagan had requested to transfer out of the 911 center, partly because of mandatory overtime, union officials have said. She voluntarily accepted a demotion to a different county department on April 13, which included a pay cut from $22.65 an hour to $19.81 an hour.

County Executive Kathleen Falk released a statement last month saying the three-day suspension was "appropriate." Her chief of staff Topf Wells said Monday the county has no further comment at this time.