She says she didn't know whether to run or hide when she heard shots about 10 a.m. Wednesday.
The La Crosse Tribune reports that a 911 call came in around 10:30 a.m. local time and the Middleton Police Department "issued an alert at 11:15 a.m., advising people in buildings in the area to lock doors, stay inside and shelter in place until further notice".
Officers shot the gunman, whose identity was not immediately released, and moved him to a local hospital before he succumbed to his injuries. She didn't have any other information about the shooting but said it was "totally unexpected".
The State Journal newspaper reports that one woman was taken out of the building screaming, saying it was "a devastating loss" and being held up by another person.
She said she knew that one co-worker had been grazed by a bullet but was OK.
Reports say the shots were fired at Esker Software. Police and multiple ambulances have responded.
Lahmers told the Associated Press she ran out of the building and hid behind a vehicle.
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Officials say the suspect in a Wisconsin workplace shooting that injured four people has died after being shot by police.
She said the building's glass entrance door was shattered. We're all software people.
The suspect was shot by officers after the incident at WTS Paradigm, a software company, Middleton Police Chief Charles Foulke said at a news conference. He says he then saw numerous people running away from the building in "full sprint". Others remained huddled in a cafeteria for more than an hour.
An employee at WTS Paradigm, who witnessed the shooting, told the Wisconsin State Journal that the gunman was also an employee with the company. The company's website was down Wednesday.
A shopping center next to the building was temporarily put on lockdown at the direction of police.
The office is located at 1850 Demming Way in Middleton, located about seven miles west of Madison and 90 miles west of Milwaukee.