MADISON, Wis. -- A 911 dispatcher received a call from the cell phone of a University of Wisconsin-Madison student sometime before she was killed last month but the call was apparently ignored, according to officials.

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An official with the Dane County Public Safety communications said Thursday that a call for service was made from Brittany Zimmermann's apartment to 911 on the day that she was killed in early April, but mistakes in how the call was handled resulted in no police officers being sent to investigate.

Dane County Executive Kathleen Falk said an investigation into what happened is currently under way, although city and county officials were disputing each other in two different press conferences, WISC-TV reported.

Confusion still surrounds the question of whether help should have been sent. While 911 officials said that the dispatcher essentially heard nothing to indicate an emergency, police are saying that there was evidence of an emergency on this call that should have prompted her to dispatch officers.

Madison police pointed a finger directly at Dane County 911 Center and unequivocally said officers should have been sent to Zimmermann's West Doty Street home after she apparently placed a call for help.

However, 911 officials said that that nothing during that call indicated an emergency was occurring and so the dispatcher hung up.

Joe Norwick, the director of Public Safety Communications who heads the 911 Center, said that that the dispatcher did fail to call the number back, which violates policy. He said that the dispatcher said she forgot to because she had two other 911 calls to answer at the time.

"In this case, there were other 911 calls waiting," he said. "I don't know what type of emergencies were waiting in the queue. And this person went on to answer other 911 calls."

Norwick said that it's unclear that even if the dispatcher had made the call back, help would have been sent. This is because determining exact locations of cell phone calls is tricky and he said that police policy isn't to send officers to follow up on hang-up calls from cell phones.

Police said that they learned the day of Zimmermann's death that a 911 call had been placed from her phone. Police Chief Noble Wray said in a news conference on Thursday that they then told the 911 Center about it, requested they not released or discuss it, and later recommended to 911 officials that they do an investigation into what went wrong:

"The 911 Center did not call back to the telephone number. Madison Police Department was not notified of the call and an officer was not sent," he said.

Norwick said that their policies in terms of returning calls depend on the circumstances.

"It depends on the calls and what we know and what can we know and ascertain and what our policies are," Norwick said. "Again, in this case, there were other 911 calls waiting."

He said that when the dispatcher received the call, she inquired several times to determine whether an emergency existed and received no answer to the inquiries.

Norwick didn't say if anything was heard from that cell phone call, what time it was placed or how long the call was, citing an order from Madison police because of the ongoing investigation. Neither 911 officials nor the police will release the tapes.

Wray said that it's too early to know whether a better response could have prevented Zimmermann's killing or helped capture her killer. He said that he's concerned about the way it was handled. He said that he thinks the call contains evidence that should have been enough for the dispatcher to take it seriously and dispatch a police officer.

Norwick said Thursday that he's not sure if the dispatcher will be disciplined. He didn't rule out disciplining her, but characterized her as an experienced employee with a good record and a caring person.

He said that the 911 Center typically receives about 400 calls a day and about 10 to 15 percent are hang-up calls.

County Officials Defend 911 Center

County Executive Falk and Dane County Sheriff Dave Mahoney on Thursday both defended the protocols in place at the 911 Center.

They said that the policy on any hang-up in Dane County is to call the number back and the procedure for sending out officers depends on the call.

They said that technological limitations influence the existing policy. They said calls from land phone lines offer a number and an address for officers to go to, but they're not always able to pinpoint a location with a cell phone call.

"If there's no voice, no one talking, what do you do?" Mahoney said. "We rely upon dispatchers to listen for sounds that an emergency is taking place."

Falk said that they're always reviewing best practices for handling the calls, but that law enforcement officials are typically determining how they want dispatchers to respond.

"Until they tell us to handle a situation differently, we will continue to follow the policy they've directed," she said.

Falk said that if any law enforcement wants to change the county's policy, she is open to starting those discussions.

Dispatchers Say Cell Calls Categorized Into 3 'Phases'

According to area dispatchers, emergency calls made on cell phones fall under three "phases," which were developed by the Federal Communications Commission (FCC).

In Phase Zero, the dispatcher receives only the caller's phone number. In Phase 1, the dispatcher can identify the specific cell phone tower where the call is coming from. In Phase 2, dispatchers are usually able to locate the caller's phone using global positioning system (GPS) technology within 300 meters.

Newspaper Reports Alleged Theory Of Student's Slaying

Meanwhile, Isthmus, Madison's alternative weekly reported on Thursday that police investigators think Zimmermann was stabbed and beaten to death inside her West Doty Street apartment on April 2. Police said the UW-Madison junior was killed after her assailant broke into her first-floor apartment. Zimmermann's fiancé later found the woman's body in the two-flat house that they shared. Police said that the fiancé isn't considered a suspect.

Authorities are still searching for her killer and haven't arrested anyone in connection the case.

Stay tuned to WISC-TV and Channel 3000 for continuing coverage.

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