In 1892, she married George Barker in Lawrence County, Missouri, and the couple had four sons: Herman (1893–1927), Lloyd (1897–1949), Arthur (1899–1939), and Fred (1901–1935).

The 1910 to 1930 censuses and the Tulsa City Directories from 1916 to 1928 show that George Barker worked in a variety of generally low-paying jobs.

[1] Barker's sons committed crimes as early as 1910, when Herman was arrested for highway robbery after running over a child in the getaway car.

According to writer Miriam Allen deFord, George "gave up completely and quietly removed himself from the scene" after Herman's death and the imprisonment of his other sons.

After a series of robberies, Fred and Karpis killed Sheriff C. Roy Kelly in West Plains, Missouri on December 19, 1931, an act that forced them to flee the area.

Racketeer, Jack Peifer, suggested that they move to St. Paul, Minnesota, which had a reputation at the time as a haven for wanted criminals.

The gang operated under the protection of St. Paul's police chief Thomas "Big Tom" Brown, and they went from being bank robbers to kidnappers under his guidance.

[5] Ma's common-law husband Arthur Dunlop was said to be loose-lipped when drunk, and he was not trusted by members of the gang; Karpis described him as a "pain in the ass".

[6] While at one hideout, a resident identified the gang from photographs in True Detective magazine and told the police, but Chief Brown tipped them off and they escaped.

[6] Chief Brown's involvement in the gang's escape could not be proven, but he was demoted to the rank of detective and was later dismissed from the police force altogether.

[7] The gang relocated to Menomonie, Wisconsin, and Fred Barker hid Ma in a variety of hotels and hideouts during their stay there.

[8] The gang decided to leave St. Paul with the FBI on the case and without Tom Brown supplying information; they moved to the Chicago area, renting apartments for Ma while they tried to launder the ransom.

[9] FBI agents discovered the hideout of Barker and her son Fred after Arthur was arrested in Chicago on January 8, 1935.

The FBI identified the house where the gang were staying from references to a local alligator known as "Gator Joe", mentioned in a letter sent to Doc.

[12] Karpis has suggested that the story was encouraged by J. Edgar Hoover[15] and his fledgling Federal Bureau of Investigation (FBI) to justify his agents' killing an old woman.

[16] After her death, Hoover claimed that Ma Barker was "the most vicious, dangerous, and resourceful criminal brain of the last decade".

"[4] Alvin Karpis was probably the real leader of the gang, and he later said that Ma was just "an old-fashioned homebody from the Ozarks … superstitious, gullible, simple, cantankerous and, well, generally law abiding".

There is not one police photograph of her or set of fingerprints taken while she was alive… she knew we were criminals but her participation in our careers was limited to one function: when we traveled together, we moved as a mother and her sons.

[6] Writer Tim Mahoney argues that the real force behind the gang was the corrupt St. Paul law-enforcement system, especially under Police Chief Tom Brown.