CHICAGO - An Uber driver who went on a shooting spree that killed 6 people in the Midwestern US state of Michigan pleaded guilty to all charges Monday.

In a surprise turn as the trial was scheduled to begin, Jason Dalton pleaded guilty to embarking on a deadly February 2016 shooting spree in the small city of Kalamazoo, in between driving for customers of the ride-sharing service Uber.

Dalton was charged with 6 counts of murder, 2 counts of attempted murder and 8 firearms charges. He faces a mandatory life sentence without parole.

Prosecutors said no deal was offered for the guilty plea.

When asked by the presiding judge whether he was pleading guilty "voluntarily of your own free will," Dalton replied: "Yes. I've wanted this for quite a while."

Dalton reportedly had told police that he was made a "puppet" by the Uber application, which directed him to shoot people at random over the course of several hours.

His victims were a 25-year-old mother wounded while shielding a group of children from bullets, a father and son fatally shot at a car dealership and four senior citizens killed in a restaurant parking lot where a teen was also wounded.

NBC television affiliate WOOD reported that Dalton chose to plead guilty to spare his family and victims' families the ordeal of a trial.