Police say it all began shortly after 8:30 p.m. when the suspect, an employee named Yvonne Hiller, was suspended from her job and escorted from the plant in the 12000 block of Roosevelt Boulevard.
About 10 minutes later she allegedly came back, crashed her car into a fence outside the plant, and entered the building armed with a .357 Magnum.
Police say Hiller then shot a female co-worker in the back of the head, killing her, and went on to shoot another woman and a man.
That woman also died, while the man was rushed to Aria-Torresdale Hospital in critical condition. The man was shot in the chest, and reports indicate he may have also been shot in the neck. His name has not yet been released.
As people were being cleared out of the building, SWAT teams were able to locate Hiller on the second floor. She was taken into custody at around 9:39 p.m., a little more than an hour after it all began.
"As a result of phone calls from some people who were trapped in the room with her - on a side room, to let us know where she was - SWAT made entry, and she surrendered at that time," said Philadelphia Police Commissioner Charles Ramsey.
Ramsey said seven people were hiding near where the woman was found, and as many as 100 people were in the plant at the time of the shooting.
Ramsey also said one shot was fired at police through a wall, but no officers were injured.
The shooting happened on the third floor of the plant where the mixing department is located. Hiller worked in that department of the building and has worked at the plant for 15 years.
Sources say Hiller has been imagining that her coworkers were doing strange things to her including spraying deer urine on her clothing and other instances the company could not confirm.
Sources say Hiller believed the female victim who was shot in the head was her main antagonist.
Reports indicate she was once suspended for using abusive language on a voicemail to a supervisor.
Reports also say coworkers have complained that the suspect was in need of psychiatric help, but the company said the only way she could be forced to receive help was if she threatened someone.
A man whose aunt works in the plant said, after the shootings, the rest of the workers ran for cover.
"She said this lady that works there came in and just wasn't herself, she walked by her two times...and the next thing you know there were gunshots going off," the man told Action News.
Police have not officially reported on motives in the shootings.
The Kraft Foods plant was formerly known as the Nabisco Factory.