The Frederick County house where a mother, father and infant boy were fatally shot Wednesday. Police say the father shot his wife as she was holding their infant son, killing both, before he killed himself. (Lynh Bui/The Washington Post)

An argument between a Frederick County couple ended with the husband shooting and killing his wife as she was holding their infant son, the sheriff’s office said.

The bullet went through the mother and fatally struck her 3-month-old boy before the husband shot and killed himself, officers said.

The Frederick County Sheriff’s Office on Monday released the details of the murder-suicide, which happened last week on a quiet, wooded cul-de-sac in southern Frederick County.

The incident began Wednesday as Barbara Giomarelli, 42, took her 5-year-old daughter upstairs to a give her a bath. As she was filling the tub, sheriff’s officers said, her husband — Benyam Asefa, 40 — came into the bathroom and an argument began.

“Why the parents were arguing that evening is unknown,” a sheriff’s office statement said.

The parents subsequently left the bathroom and went downstairs, where Asefa shot Giomarelli with a 9mm handgun. The sheriff’s office said the “projectile exited” her while she was cradling her baby, Samuel Asefa, on her shoulder.

Asefa apparently shot Giomarelli at an angle and the bullet “entered the right side of her skull and exited, going into the child’s skull,” according to the sheriff’s office. The bullet ultimately lodged in a nearby wall.

Asefa at some point turned the gun on himself, sheriff’s officers said.

The 5-year-old daughter stayed in the bathtub for some time, officers said, before she got out, dressed herself and went downstairs, where she found her family members. She left the home and walked to a neighbor’s house. She told the neighbor that her family was hurt inside her home. The neighbor called 911 about 8:15 p.m.

The sheriff’s office said the young girl had “no knowledge of what had occurred on the first level of the home while she was in the bathtub.”

The girl was placed in the care of a family friend in the area after being with child protective services, according to the sheriff’s office.

Officers said they think the shooting took place between 6 p.m. and 8 p.m. The mother and baby were found in the kitchen, and Asefa was found in the living room area, next to the kitchen.

The sheriff’s office said Giomarelli sent an e-mail at 6 p.m. to a friend that was “a normal conversation.”

“There was nothing that indicated there was any issues whatsoever,” said Capt. Tim Clarke of the sheriff’s office. “There was no indication anything bad was taking place at that point.”

Investigators received reports in interviews with family members and friends that there were “domestic issues in the past” between the couple, but none were reported to authorities.

Asefa, who had a PhD, was most recently employed as a clinical immunologist for the Lovelace Respiratory Research Institute, working in support of the National Institute of Allergy and Infectious Diseases Integrated Research Facility in Frederick, according to the National Institutes of Health. But his job was eliminated Sept. 30 because of cost-cutting, according to the sheriff’s office.

Giomarelli, an Italian national, had worked at the University of Maryland’s Institute of Marine and Environmental Technology in Baltimore on a visa for three years, said Alex Likowski, a spokesman for the University of Maryland at Baltimore. She left the job in February, he said.

Officers said she was to start a job Dec. 2, but they did not know where.

Frederick County typically records one or two homicides a year, and news of the three deaths sent shock waves through the Lake Linganore community.