Question: What member of the Barker-Karpis gang was Walter Walsh involved in the capture of?

Context paragraphs:
Rudolf Schrader: Rudolf "Rudy" Schrader (also spelled Rudolph) (March 17, 1875 – January 18, 1981) was an American gymnast who competed at the 1904 Summer Olympics in St. Louis.  As a member of the Turnverein Vorwärts club he placed seventh in the team all-around and participated in three individual events, his best finish being 68th in the gymnastic triathlon.  Born in Germany, Schrader moved to the United States at the age of 15 and worked as a cabinetmaker while training as a gymnast.  After the Olympics he joined Sears and remained with them until his retirement at the age of 65.  Until he was surpassed by Walter Walsh in March 2013, Schrader was the longest-lived Olympian, having died in January 1981 at the age of 105.

Arthur Barker: Arthur R. Barker (June 4, 1899 – January 13, 1939) was an American criminal, the son of Ma Barker and a member of the Barker-Karpis gang, founded by his brother Fred Barker and Alvin Karpis.  Generally known as "Doc", Barker was typically called on for violent action, while Fred and Karpis planned the gang's crimes.  He was arrested and convicted of kidnapping in 1935.  Sent to Alcatraz Federal Penitentiary in 1936, he was killed three years later while attempting to escape from the Rock.

Fred Barker: Frederick George Barker (1901–1935) was one of the founders of the Barker-Karpis gang, which committed numerous robberies, murders and kidnappings during the 1930s.  He was the youngest son of Ma Barker, all of whose children were criminals.  He was killed in a lengthy gunfight with the FBI in 1935.

Kidnapping of Edward Bremer: The Kidnapping of Edward Bremer was the last major criminal enterprise of the Barker-Karpis gang.  Though successful in netting the gang a large ransom, it brought down the full force of the FBI on the gang, resulting in the death or capture of its main members in the months afterwards.  The kidnapping was organized by racketeer Harry Sawyer, and the principal kidnappers were Fred Barker, Alvin Karpis, Arthur Barker, Volney Davis and George Ziegler.

Tom Brown (police chief): Thomas Archibald Brown (1889–1959), known as "Big Tom", was police chief of St. Paul, Minnesota in the 1930s.  During his time in office he presided over a period of unprecedented corruption in which he assisted several major criminals, notably the Barker-Karpis gang and John Dillinger.

Walter Walsh (courtier): Walter Walsh (fl.  1530) was a courtier and Groom of the Privy Chamber at the court of Henry VIII of England.  In November 1530, Cardinal Wolsey surrendered the Great Privy Seal to Walsh and Henry Percy, 6th Earl of Northumberland, when they arrived to remove it from him.

Walter Walsh (disambiguation): Walter Walsh was an FBI agent and Olympic shooter.

Joseph P. Moran: Joseph P. Moran (1895–1934) was an American doctor known for catering to the Depression-era criminal underworld in the early 20th century.  He was also a peripheral member of the Barker-Karpis gang, and was possibly the last physician to see the mortally wounded John Hamilton, a member of the John Dillinger gang, whom Moran refused to treat.

Walter Walsh: Colonel Walter Rudolph Walsh (May 4, 1907 – April 29, 2014) was an FBI agent, USMC shooting instructor and Olympic shooter.  Walsh joined the FBI in 1934, serving during the Public enemy era, and was involved in several high-profile FBI cases, including the capture of Arthur Barker and the killing of Al Brady.  He served in the Pacific theatre during World War II with the Marine Corps and, after a brief return to the FBI, served as a shooting instructor with the Marine Corps until his retirement in the 1970s.

Barker–Karpis gang: The Barker-Karpis Gang was one of the longest-lived criminal gangs during the Depression Era, spanning from 1931 to 1935.  The gang was founded by Fred Barker and Alvin Karpis, and later joined by Fred's brother Arthur "Doc" Barker.  Along with the three core members, the gang's network spanned up to 25 members at one point.

Supporting paragraphs: Walter Walsh Arthur Barker
Answer: Arthur Barker