A Michigan man who worked as an Uber driver has been denied bail at a hearing on 22 February over the fatal shootings of six people in Kalamazoo at the weekend, as police searched for a motive in a case that raised questions about how the car service vets its drivers.

Jason Dalton, 45, who faces 16 charges, including six of murder, which can carry a sentence of up to life in prison, made his first court appearance via video link. He did not enter a plea. He was seen on a monitor at the Kalamazoo County jail wearing glasses and dressed in an orange prison jumpsuit flanked by two prison guards.

When asked if he had a message for the community, Dalton said that he preferred to "remain silent". The judge denied bail and set 3 March as the date for the next hearing.

Prosecutors allege Dalton drove from one place to another, randomly shooting victims over a five-hour period on 19 February. The locations include an apartment complex, a car dealership and a Cracker Barrel restaurant in Kalamazoo, about 150 miles west of Detroit.

Police were investigating reports that Dalton apparently picked up passengers for Uber in between the shootings.

Two people were wounded, including a teenage girl, who was initially thought to have died. No motive has been given for the attacks.

Initial checks with a federal agency and legal advocacy organisation Southern Poverty Law Center indicate Dalton was unknown to both law enforcement and counter-terrorism agencies for having any kind of known connection to extremist groups.