It was a summer morning last July when 64-year-old Mairi Morrison set out for her daily walk, not knowing it would be her last.

Surveillance video shows a USPS mail truck pulling out of a gas station in Kensington, Maryland, right as Morrison was crossing the driveway.

After the USPS driver hit Morrison, he kept driving forward for 4 seconds and then backed up for 6 seconds, all with her body still underneath the van, according to court documents.

“I feel her loss every single day and I try not to imagine, but it’s not easy, how painful and horrific her death ended up being,” Morrison’s sister, Catriona Morrison, told News4 by phone.

The driver of the mail truck was 26-year-old Oscar Pedrozo from Silver Spring. Montgomery County prosecutors have now charged him with criminally negligent manslaughter, a misdemeanor.

Court documents show Pedrozo told police in an interview he heard a thump and felt a vibration, and thought someone ran into him.

He admitted he had earbuds in and was listening to music, but he said the volume was low and that he could still hear his surroundings.

“I am relieved the driver is being held responsible. I also feel, of course, sadness and a renewed sense of how much has been needlessly lost,” Catriona Morrison said.

Mairi Morrison was an attorney. Her sister said she enjoyed reading, traveling and giving pro-bono legal assistance.

“If somebody needed legal help, she would just throw herself into the cause and work tirelessly for them free of charge,” she said.

Court records show Pedrozo posted bond on Thursday.

If convicted, he could face up to three years behind bars.

Pedrozo’s trial is scheduled for May 14.

“The individual is still an employee with the U.S. Postal Service,” USPS said in a statement to News4. “Pursuant to postal policy, we do not discuss internal personnel matters, and we cannot further comment on the status of this employee.”