A 21-year-old woman found shot to death in her car last month in Willingboro was trying to sell a used phone and was killed during a meeting arranged online by a man who was arrested and charged Tuesday, Burlington County Prosecutor Scott Coffina said.

Marvin A. Coleman Jr., 20, of Willingboro, was arrested during a traffic stop Tuesday afternoon near his home on Marlboro Lane and was later charged with first-degree murder and related offenses, Coffina said.

The motive for killing Maribely Lopez of Lindenwold was still under investigation. The phone that Coleman ostensibly wanted to purchase was found inside Lopez’s Ford Focus.

Police were called the morning of March 7 to Medley Lane and found Lopez dead inside her car with the engine still running. Investigators believe she had been shot the night before.

Coffina said the proposed transaction was arranged by Coleman on the OfferUp marketplace app and the meeting place was in front of a vacant house on Medley near Coleman’s residence.

“People selling items online to strangers should exercise appropriate caution, such as utilizing safe transaction zones that many of our local police departments maintain in the parking lots of their stations,” Coffina said.