NASHVILLE, Tenn. (WTVF) — Wednesday marks one year since a man was killed while driving to work.

On November 20, 2018, Joe Shelton was driving to work on Interstate 24 when a 23-pound piece of concrete fell onto his car. The slab crashed through his windshield, killing Shelton. A year later, his family is still without answers on how it happened.

Metro Nashville police said they’re trying to determine if someone threw the rock or if it may have fallen off and onto the car from the Shelby overpass.

Investigators still want to identify this man, who was in an Exxon Tiger Mart near the Shelby Avenue Bridge just after the incident. They say he was in the market for several minutes and got a cup of coffee.

Police hope he can help bring some closure to the family.

If you know anything about the incident, you are encouraged to call Metro Nashville Police Department's Crimestoppers at 615-74-CRIME.

Read more: Family still searching for answers one month after man killed by falling concrete