The Justice Department has begun work on a legal memo recommending no civil rights charges against a white police officer in Ferguson, Missouri, who killed an unarmed black teenager in August, law enforcement officials said.

That would close the politically charged case in the shooting death of 18-year-old Michael Brown. The investigation by the F.B.I., which is complete, found no evidence to support civil rights charges against the officer, Darren Wilson, the officials said.

A broader civil rights investigation into allegations of discriminatory traffic stops and excessive force by the Ferguson Police Department remains open, however. That investigation could lead to significant changes at the department, which is overwhelmingly white despite serving a city that is mostly black.