A gun found along the Capital Beltway helped lead detectives to arrest a Mississippi woman in the June 2012 fatal shooting of a Silver Spring man with whom she said she’d been in a romantic relationship, police said.

Katrina Renee Ben, 35, was charged with first-degree murder in the killing of Eric Somuah, who was shot in the head inside his Silver Spring apartment, Montgomery County police said.

Somuah, 34, who had worked at a Bethesda Range Rover and Jaguar dealership, failed to show up for work and didn’t respond to phone calls and text messages. His worried family called police, who found his body June 6, 2012, inside his locked apartment.

Soon after the killing, detectives interviewed Ben, who was then a neighbor of Somuah’s, police said. She was the last person known to have been in Somuah’s apartment, they said, and told police that she and Somuah were romantically involved.

The case went unsolved for months. But police said a break came from a partially disassembled gun that was found by a resident the day after the killing on the shoulder of Interstate 495 near Colesville Road. Authorities said ballistics tests linked the weapon to a bullet from Somuah’s body.

Detectives probed deeper, police said, and found that Ben had bought a gun at a pawn shop in 2004 and that the make, model and serial number match the discarded weapon.

Police did not release a motive in the case and Somuah’s family had not been given all of the details about Ben’s arrest, Michael Somuah, the victim’s brother, said.

Still, he said the discovery of the gun “was miraculous.”

Ben, who was staying with her father at his Mississippi home when she was arrested Friday, is a traveling nurse who is between jobs, her father, Robert Gray, said. He said he does not think hhis daughter shot Somuah.

“Katrina wouldn’t hurt a fly,” he said. “Her whole life she didn’t have a bad record.”

According to Gray, the relationship between Ben and Somuah was not serious.

Gray said his daughter told him that she had left Somuah in his apartment with someone she didn’t know. The next morning, she tried to call Somuah, but he never responded, according to her father’s account. “She found out later he had been murdered. If she hadn’t gone to work, she’d have been killed herself,” he said.

Ben was jailed in Mississippi pending extradition to Montgomery, police said.

In the days after his brother’s death, Michael Somuah recalled that he had spoken with his brother on the evening that his family last had contact with him. His brother put a woman on the phone to say hello, Michael Somuah recounted at the time, but he was reluctant to discuss the call further because no arrest had been made.

On Tuesday, Michael Somuah said he thinks the woman he spoke with was Ben, based on information from his brother, who had said she was a traveling nurse.

His brother was making plans to start a company to staff health-care positions, Michael Somuah said.

Michael Somuah said the arrest came a year to the day after his brother’s funeral. “It was crazy, unbelievable to hear it on the very day of that anniversary,” he said.

Mary Pat Flaherty contributed to this report.