Why did the defense have Ms. Moore testify?

During the trial, Asa Briggs uses Dorthy Moore as a witness to testify that James King was at her house during the robbery.She tells Briggs that James was at her home around three thirty. When Petrocelli cross-examines Moore, Dorthy mentions that she is James' cousin. Dorthy also says that James visited her about twice a month and was simply dropping off a lamp which happened to be a Christmas present. Petrocelli then asks her...

During the trial, Asa Briggs uses Dorthy Moore as a witness to testify that James King was at her house during the robbery. She tells Briggs that James was at her home around three thirty. When Petrocelli cross-examines Moore, Dorthy mentions that she is James' cousin. Dorthy also says that James visited her about twice a month and was simply dropping off a lamp which happened to be a Christmas present. Petrocelli then asks her the cost of the lamp and if she remembered whether James was working at the time. Dorthy Moore cannot recall the price of the lamp or if James was employed. However,  Dorthy insists that she isn't lying but continues to struggle when she is asked questions about James' life. Petrocelli then asks Dorthy if she still has the lamp, and Moore says that she does not have it because it broke. Asa Briggs uses Moore's testimony as an alibi that James King was not near the store during the crime.