Question: Mike Gibbons was an American boxer who claimed the Middleweight Champion of the World status following what Polish American professional boxer's murder?

Context paragraphs:
Dan Creedon: Dan Creedon (June 9 1868 - July 10 1942) was a middleweight boxer who challenged for the world middleweight title twice and claimed the title between 1895 and 1897.  Creedon was born in Invercargill, New Zealand but his boxing career developed in Melbourne, Australia.  Like many of Australia's best boxers of this era, Creedon was taught by boxing pioneers Jem Mace and Larry Foley.  He held the Australian middleweight title from 1891 until his departure for America in 1892.  He challenged Bob Fitzsimmons for the world middleweight title in 1894, in what would be Fitzsimmons' last defense of his belt before becoming a heavyweight.  Creedon was knocked out in just 2 rounds.  However, a year later he claimed the world title following his victory over Frank Craig in London.  Creedon defended his claim to the title at least twice, but he is not commonly recognized as a middleweight champion by boxing historians.  He would eventually lose to Kid McCoy, after which his career took a downward spiral.

Mike Gibbons: Mike Gibbons (July 20, 1887 in St. Paul, Minnesota – August 31, 1956) was an American boxer from 1908 to 1922.  The brother of heavyweight Tommy Gibbons, Mike claimed Middleweight Champion of the World status in 1909 following Stanley Ketchel's murder.  Although he never won the title, Gibbons is regarded as one of the all-time best welter and middleweight boxers by historians.  Statistical boxing website BoxRec lists Gibbons as the #18 ranked middleweight of all time, while "The Ring Magazine" founder Nat Fleischer placed him at #9.  The International Boxing Research Organization rates Gibbons as the 17th best middleweight ever and boxing historian Bert Sugar placed him 92nd in his Top 100 Fighters catalogue.  Gibbons retired due to deteriorating vision.  Following his boxing career he entered business in his native St. Paul, and became a member of the Minnesota Athletic Commission.  Gibbons was elected to the Ring Magazine Hall of Fame in 1958, the International Boxing Hall of Fame in 1992, the World Boxing Hall of Fame in 1997, and the Minnesota Boxing Hall of Fame in 2010.

Mike O'Dowd: Michael Joseph O'Dowd (April 5, 1895 in St. Paul, Minnesota – July 28, 1957) was an American boxer who held the World Middleweight Championship from 1917 to 1920.  He won the title on November 14, 1917 by knocking out Al McCoy in the sixth round after dropping him six times.  O'Dowd was the only active boxing champion to fight at the front during World War I (1918, while serving in the U.S. Army).  During his career he claimed victories over Hall of Famers Jack Britton, Mike Gibbons, Kid Lewis and Jeff Smith.  On February 25, 1918, he held the legendary Harry Greb to a draw.  O'Dowd was knocked out just once in his career, his last fight on March 16, 1923.  He was inducted into the Minnesota Boxing Hall of Fame in 2011 and the International Boxing Hall of Fame in 2014.

Jamie Moore (boxer): Jamie Moore (born 4 November 1978) is a British former professional boxer.  He is a former European light middleweight champion, a two-former British light middleweight champion and a former Commonwealth light middleweight champion.

Stanley Ketchel: Stanisław Kiecal (September 14, 1886 – October 15, 1910), better known in the boxing world as Stanley Ketchel, was a Polish American professional boxer who became one of the greatest World Middleweight Champions in history.  He was nicknamed "The Michigan Assassin."  He was murdered at a ranch in Conway, Missouri, at the age of 24.

Jermain Taylor: Jermain Taylor (born August 11, 1978) is an American former professional boxer who competed from 2001 to 2014.  He remains the most recent undisputed middleweight champion, having won the WBA (Undisputed), WBC, IBF, WBO, "Ring" magazine, and lineal titles in 2005 by beating Bernard Hopkins, and in doing so ending Hopkins' twelve-year reign as middleweight champion.  This made Taylor the first boxer in history to claim each title from all four major boxing sanctioning organizations in a single fight (Hopkins had won his world titles separately between 1995 to 2004).  He has also held the IBF middleweight title twice.

Kali Reis: Kali Reis is an American professional female boxer.  She is the first professional Native American boxer to hail from New England, and the first Native American fighter to win the International Boxing Association (IBA) middleweight crown.  She is also a former WBC World Middleweight Champion and WIBA World Champion.

Natascha Ragosina: Natalia Yurievna Ragozina (Russian: Наталья Юрьевна Рагозина ), better known as Natascha Ragosina, is an undefeated retired professional boxer who spent much of her career ranked as the top female super middleweight in the world.  Though born in Kazakhstan (formerly a part of the Soviet Union) and currently residing in Moscow, she competed professionally for Russia and is of Russian descent.  She is the longest reigning WBA female super middleweight champion and WBC female super middleweight champion.  At the time of her retirement, she held all major female super middleweight titles and two heavyweight belts:

Jeff Smith (boxer): Jerome "Jeff Smith" Jefferds (April 23, 1891 – February 3, 1962) was an American professional boxer who held the Australian version of the World Middleweight Title during his career.  Despite his relative anonymity, Smith faced off against some the best fighters of his era, including Harry Greb, Gene Tunney, Mike Gibbons, Georges Carpentier, Les Darcy and Tommy Loughran.  Statistical boxing website BoxRec lists Smith as the 17th greatest middleweight ever, while Ring Magazine founder Nat Fleischer ranked Smith as the #10 Middleweight of all-time.  He was inducted into the Ring Magazine Hall of Fame in 1969 and the International Boxing Hall of Fame in 2013.

Sugar Ray Seales: "Sugar" Ray Seales, (born September 4, 1952) was the only American boxer to win a gold medal in the 1972 Summer Olympics.  As a professional, he fought middleweight champion Marvin Hagler three times.  He is also the former NABF and USBA middleweight champion.

Supporting paragraphs: Mike Gibbons Stanley Ketchel
Answer: Stanley Ketchel