After an Uber driver allegedly killed six people in a shooting rampage in Michigan, attention has turned to how the ride-sharing app screens potential drivers.

Jason Brian Dalton, who picked up and dropped off passengers during his alleged shooting spree, allegedly killed six people and wounded two others in Kalamazoo, Michigan, on Saturday night, authorities said.

Uber bills itself as a safe ride, with prospective drivers needing to pass a background check to become part of the platform.

According to Uber’s website, anyone applying to be an Uber driver must give detailed information such as their full name, birthdate and Social Security number. They also need to provide a copy of their driver’s license, auto insurance and vehicle registration.

Uber then uses background investigation service Checkr to conduct a Social Security trace that identifies addresses associated with an applicant. These are cross-referenced with various national and state databases to check for offenses.

When a criminal record is identified, the record is either pulled up digitally or reviewed in-person by someone from Checkr.

Applicants are disqualified if they appear on any sex offender registry, are suspected terrorists or have had felony convictions.

The ride-sharing app has been criticized by taxi unions for its lack of fingerprint scanning, something the company continues to resist.

However, in the case of the Kalamazoo suspect, who had a clean record, it’s unclear how a more thorough background check could have prevented the violent attacks.