The garbage truck incident that killed a Baltimore sanitation worker Friday was the result of what is believed to be “driver error,” according to two sources with direct knowledge who were not authorized to speak because of the ongoing investigation.

Timothy Cartwell was working in an alley along the 1800 block of Baker Street around 10:30 a.m. as part of a three-man crew when the driver of the garbage truck backed into him, pinning him against a wooden light pole, the sources said. The driver, who has not been named, did not know Cartwell was behind the garbage truck, the sources said.

“The circumstances surrounding the death of Bureau of Solid Waste worker Timothy Cartwell remain under active investigation by the Baltimore Police Department,” DPW spokeswoman Jennifer Combs said by email. “We are fully cooperating with BPD’s investigation to ensure a complete and accurate understanding of what occurred.”

It’s not clear what training or operating procedures are required for DPW garbage truck drivers.

A police spokesperson did not have further information to share.

Garbage trucks have significant blind spots because of their design. Some newer city trucks have rear view cameras but it appears this one did not, according to the sources.

Salary records show Cartwell was a long-time DPW employee, having worked in sanitation since at least 2007.

Friday’s incident marked the second time in about three months that there was a work-related death of a Baltimore sanitation worker. Ronald Silver II died in August from heatstroke, prompting outrage from labor unions and some City Council members. Mayor Brandon Scott hired a Washington-based law firm to review DPW’s workplace safety policies, and the firm’s report found the agency had no plan for dealing with heat illnesses.

That report found employees who reported unsafe conditions feared retaliation from their supervisors, including more onerous working conditions or being assigned demeaning tasks.

AFSCME Maryland Council 3, the union that represents employees of multiple city agencies, issued a statement over the weekend that said Cartwell’s death showed “far more needs to be done” on workplace safety.

“We have been demanding a variety of health and safety information from the city as well as negotiation to enhance the training and protection of the workforce,” the statement said.

Soon-to-be City Council President Zeke Cohen said he will direct the council to “find answers” about Cartwell’s death and will hold DPW “fully accountable.”

The Scott administration is aware of the myriad issues plaguing the public works department and has pledged improvement. Scott called Cartwell’s death devastating in a social media post.