WASHINGTON —The Justice Department enters its court fight against the city of Ferguson with the apparent upper hand, given a months-long investigation that found vast problems in the way police and courts treat poor people and minorities in the St. Louis suburb.

In suing the city, which took a high-stakes gamble by rejecting a settlement with the federal government, the department will look to prove in court the same constitutional violations it’s already alleged on paper: Baseless stops and searches of black drivers, excessive use of force by officers and a profit-driven court system reliant on fines for petty violations.

“They have a very solid case,” Samuel Bagenstos, the former No. 2 official in the Justice Department’s Civil Rights Division, said.