A fourth developer has pleaded guilty in the sweeping Prince George’s County corruption scandal, Maryland U.S. Attorney Rod J. Rosenstein announced Monday.

Karl Granzow, 46, a former high-ranking official in the county fire department, pleaded guilty in federal court March 30 to charges of conspiracy to extort public officials in connection with a development project and income tax evasion.

Granzow pleaded guilty under seal. Granzow pleaded guilty in connection with a proposed development project for apartment buildings, retail space and offices near the Greenbelt Metro Station.

Former county executive Jack B. Johnson and his wife Leslie Johnson, a member of the county council, have both pleaded guilty to felony charges in connection with the broad probe.

Leslie Johnson (D-Mitchellville), who admitted hiding $79,600 in cash when she pleaded guilty last month to witness and evidence tampering, has said she will resign her seat on the county council on July 31. Granzow provided “things of value,” such as money, meals, drinks, airline tickets, rounds of golf, mortgage payments, employment, and in-kind campaign contributions worth between $30,000 and $70,000 to state and local candidates, according to federal officials.

He faces a maximum penalty of five years in prison for each count. A sentencing date has not been set.

The other developers to plead guilty in the scandal include:

Mirza Hussein Ali Baig, 67, a developer and Laurel doctor, paid $400,000 to $1 million in bribes to Jack Johnson and one of his appointees, James Johnson, court papers said. Baig won at least three development deals in the county during a 19-month period while Johnson was county executive, according to a 2008 Washington Post investigation of Prince George’s development deals. Baig entered a secret plea in April.

Patrick Ricker, 52, a developer and president of Ricker Brothers, was the first of the three men to be convicted, entering a guilty plea in December 2009. Ricker and Baig cooperated in the probe, according to lawyers and court papers.

Daniel I. Colton, 61, pleaded guilty to conspiracy to commit extortion and to make false statements to the Federal Election Commission, officials said.