A man shot four members of his family, killing two and injuring another two, before killing himself in a Washington, D.C. suburb, police say.

Sang Yeon Kim, 48, and Andy Kim, 10, died after they were shot in their own home in the Colesville area of Montgomery County, county police said. An 11-year-old girl and 22-year-old woman have serious injuries.

The shooter was Yong Mun Kim, police said. He shot and killed his wife and son, and wounded his daughter and adult stepdaughter. Then, he killed himself.

Officers were called to the 100 block of Amberleigh Drive just after midnight Monday for a report of multiple people shot inside a home. The caller was the 22-year-old woman.

When they officers arrived, they found the five people.

Police believe Kim planned the attack amid marital trouble. He left the names and phone numbers of relatives for police to call, officials said.

People who knew the alleged shooter were unnerved.

"Never in a million years would I ever fathom that something like this would happen. Not with him," former neighbor Jim Greene said.

The investigation is ongoing. Anyone with information for police is asked to call 240-773-5050. Callers may remain anonymous.

To find resources for domestic violence victims, visit NBC Washington's Safe at Home page.