Perkins, Santo, Barbara, along with other gang members, John True and Baxter Shorter, invaded the old lady's house. Evidently, Barbara got the gang into the house by asking to use the telephone. When the old lady either couldn't or wouldn't hand over the money and jewels, Barbara was supposed to have gone berserk.
John True testified later that Barbara lost patience and began to pistol whip Mrs. Monahan. With the other gang members cheering her on, Barbara cracked open the old lady's skull. Finally, Barbara suffocated her to death with a pillow. The gang earned nothing. There was no money and no jewelry. Perkins had been "misinformed."
-- Poe Forward
Long story short: Barbara and company got arrested and found guilty of murder. Babs proclaimed her innocence, but got caught trying to bribe a witness. She, Perkins and Santo went to the chair. Her guilt or innocence is debated to this day. (Actress Susan Hayward, who won an Academy Award for playing Barbara in the 1958 film I WANT TO LIVE!, mentioned she thought Barbara probably did it.)
Mabel Monahan (1888-1953) is buried with her husband George at Angelus-Rosedale Cemetery, 1831 W. Washington Boulevard in Los Angeles. George (1869-1940) wasn't around for Babs' arrival.
Barbara Graham - Poe Forward