Question: When did the football coach, who led the 2004 Oklahoma Sooners team,  announce his retirement?

Context articles: 1895 Oklahoma Sooners football team
2004 Oklahoma Sooners football team
Josh Heupel
Bob Stoops
List of Oklahoma Sooners head football coaches
1985 Oklahoma Sooners football team
Darrell Shepard
George Thomas (American football)
Barry Switzer Center
1956 Oklahoma Sooners football team

The 1895 Oklahoma Sooners football team represented the Oklahoma Sooners of the University of Oklahoma during the 1895 college football season and was its first football team ever fielded.
 The team completed its inaugural season with a 0–1 record.
 The Sooners played their first football game in history against a town team from Oklahoma City and lost by a final score of 34–0.
 This was the program's one and only season under the guidance of head coach John A. Harts, the next season he was gold prospecting in the Arctic.
The 2004 Oklahoma Sooners football team represented the University of Oklahoma during the 2004 NCAA Division I-A football season, the 110th season of Sooner football.
 The team was led by two-time Walter Camp Coach of the Year Award winner, Bob Stoops, in his sixth season as head coach.
 They played their home games at Gaylord Family Oklahoma Memorial Stadium in Norman, Oklahoma.
 They were a charter member of the Big 12 conference.
Joshua Kenneth Heupel (born March 22, 1978) is the offensive coordinator and quarterbacks coach for the Missouri Tigers.
 He is also a former college football player who played quarterback for the Oklahoma Sooners football team at the University of Oklahoma.
 During his college playing career, he was recognized as a consensus All-American, won numerous awards, and led Oklahoma to the 2000 BCS National Championship.
 Heupel became a coach after his playing career ended.
 He served as co-offensive coordinator for the Oklahoma Sooners until January 6, 2015, when he was fired from his position.
 He was named the assistant head coach, offensive coordinator, and quarterbacks coach at Utah State on January 23, 2015.
 After one season at Utah State, he was hired at the University of Missouri under Barry Odom's new staff.
Robert Anthony Stoops (born September 9, 1960) is a former American college football coach.
 He is the former head football coach at the University of Oklahoma, a position he held from 1999 until he announced his retirement June 7, 2017.
 During the 2000 season, Stoops led the Sooners to an Orange Bowl victory and a national championship.
The Oklahoma Sooners football program is a college football team that represents the University of Oklahoma.
 The team has had 22 head coaches since organized football began in 1895.
 The Sooners have played in more than 1,200 games in its 121 seasons.
 In those seasons, eight coaches have led the Sooners to postseason bowl games: Tom Stidham, Jim Tatum, Bud Wilkinson, Gomer Jones, Chuck Fairbanks, Barry Switzer, Gary Gibbs and Bob Stoops.
 Eight coaches have won conference championships with the Sooners: Bennie Owen, Stidham, Dewey Luster, Tatum, Wilkinson, Fairbanks, Switzer and Stoops.
 Wilkinson, Switzer and Stoops have also won national championships with the Sooners.
 Stoops is the all-time leader in games coached and won, Owen is the all-time leader in years coached, while Switzer is the all-time leader in winning percentage.
 John Harts is, in terms of winning percentage, the worst coach the Sooners have had as he lost the only game he coached.
 John Blake has the lowest winning percentage of those who have coached more than one game with .353 in his 34 games.
The 1985 Oklahoma Sooners football team represented the University of Oklahoma in the college football season of 1985–1986.
 This year was Barry Switzer's 13th season as head coach.
 The Sooners ended this season with 11 wins and a sole loss coming to the Miami Hurricanes in Norman, in a game in which the Sooners lost starting quarterback Troy Aikman for the season.
 The Sooners were forced to place their trust in lightning-quick true freshman quarterback Jamelle Holieway and a physical defense featuring three All-Americans, who led them to a Big 8 Conference title and a national championship.
 This was Oklahoma's sixth national championship and 34th conference championship in school history.
Darrell Shepard (born c. 1959) is a former American football quarterback who played for the Oklahoma Sooners from 1979 to 1981.
 Shepard is also the all-time leading passer for Odessa High School.
 In 1976, he passed for 1,156 yards and ran for 920 yards and was named to the Parade All American team.
 He is the older brother of the late Derrick Shepard and the uncle of Sterling Shepard, both of whom played for the Oklahoma Sooners during their college careers.
 His brother, Woodie Shepard, also played football for the Oklahoma Sooners.
George Carroll Thomas, Jr. (March 4, 1928 – May 23, 1989) was an American football halfback and defensive back in the National Football League for the Washington Redskins and the New York Giants.
 He was a standout high school basketball player, which led to his being recruited to play college basketball for Tulane University.
 However, first year OU football coach, Jim Tatum, convinced him stay in Oklahoma and play college football at the University of Oklahoma.
 Thomas was a standout for the Sooners, lettering in '46, '47,'48 and '49.
 He earned All-American status in 1949 List of Oklahoma Sooners football All-Americans.
 Thomas graduated from OU with a degree in Business Administration in 1950.
The Barry Switzer Center, on the University of Oklahoma campus in Norman, Oklahoma, houses football offices, the football locker room, equipment room, the Siegfried Strength and Conditioning Complex, the Freede Sports Medicine Facility and the Touchdown Club Legends Lobby.
 The Center is located at the south end of the Gaylord Family Oklahoma Memorial Stadium.
 The Barry Switzer Center, dedicated on April 24, 1999, was named after OU’s all-time winningest head football coach.
 During Summer 2015 the Switzer Center was demolished as part of the expansion of Gaylord Family Oklahoma Memorial Stadium.
 In Barry Switzer’s 16 seasons as the Oklahoma Sooners head football coach, the team won three national championships, 12 Big Eight Conference championships and eight bowl games in 13 appearances.
The 1956 Oklahoma Sooners football team (variously "Oklahoma", "OU", or the "Sooners") represented the University of Oklahoma in the 1956 college football season.
 It was the 62nd season of play for the Sooners.
 The team was led by Hall of Fame head coach Bud Wilkinson.
 They were led on offense by quarterback Jim Harris, and played their home games at Oklahoma Memorial Stadium in Norman, Oklahoma.