Scarlet Street

It's 1934. Christopher "Chris" Cross (Edward G. Robinson), a meek amateur painter and cashier for clothing retailer, J.J. Hogarth &amp; Company, is fÃªted by his employer, honoring him for twenty-five years of dull, repetitive service, from 1909-1934. Hogarth presents him with a watch and kind words, then leaves getting into a car with a beautiful young blonde.
Walking home through Greenwich Village, Chris muses to an associate, "I wonder what it's like to be loved by a young girl." He helps Kitty (Joan Bennett), an amoral fast-talking femme fatale, apparently being attacked by a man, stunning the assailant with his umbrella. Chris is unaware that the attacker was Johnny (Dan Duryea), Kitty's brutish boyfriend, and sees her safely to her apartment building. Out of gratitude and bemusement, she accepts his offer for a cup of coffee at a nearby bar. From Chris's comments about art, Kitty believes him to be a wealthy painter.
Soon, Chris becomes enamored of her because he is in a loveless marriage and is tormented by his shrewish wife Adele (Rosalind Ivan), who idealizes her former husband, a policeman who apparently drowned while trying to save a woman. After Chris confesses that he is married, Johnny convinces Kitty to pursue a relationship in order to extort money from Chris. Kitty inveigles him to rent an apartment for her, one that can also be his art studio. To finance an apartment, Chris steals $500 ($8,800 today) in insurance bonds from his wife and later $1000 ($17,700) from his employer.
Unknown to Chris, Johnny unsuccessfully tries selling some of Chris's paintings, attracting the interest of art critic David Janeway (Jess Barker). Kitty is maneuvered by Johnny into pretending that she painted them, charming the critic with Chris's own descriptions of his art, and Janeway promises to represent her. Adele sees her husband's paintings in the window of a commercial art gallery as the work of "Katherine March" and accuses him of copying her work. Chris confronts Kitty, who claims she sold them because she needed the money. He is so delighted that his paintings are appreciated, albeit only under Kitty's signature, that he happily lets her become the public face of his art. She becomes a huge commercial success, although Chris never receives any of the money.
Adele's supposedly dead first husband, Higgins (Charles Kemper), suddenly appears at Chris's office to extort money from him. He explains he had not drowned but had stolen $2,700 from the purse of the suicide he tried to save. Already suspected as corrupt for taking bribes from speakeasies, he had taken the opportunity to escape his crimes and his wife. Chris lets Higgins into his wife's room ostensibly so he can get the insurance money from his death but does so when she is asleep in the room, reasoning that his marriage will be invalidated when his wife sees her still-living first husband.
Believing he can now marry Kitty, he goes to see her, but finds out that Kitty has cheated on him. He later confronts Kitty, but still asks her to marry him; she scorns him for being old and refuses to marry him. Enraged he stabs her to death. The police visit Chris at his job, not for the murder but his earlier embezzlement. Although his boss refuses to press charges, Chris is fired. Johnny is accused of Kitty's murder.
At the trial, all of the deceptions work against Johnny, despite his attempts to implicate Chris, and Chris denies painting any of the pictures. Johnny is convicted and put to death for Kitty's murder, Chris goes unpunished, and Kitty is erroneously recognized as a great artist.
Haunted by the murder, Chris attempts to hang himself. Although rescued, he is impoverished with no way of claiming credit for his own paintings and tormented by thoughts of Kitty and Johnny being together for eternity, loving each other.

Question: why was kitty claiming that she sold them?
Answer: because she needed the money.