Boris Karloff is listed by modern sources for the role of "Murder victim" in this movie, but he was not seen in the viewed print on the Turner Classic Movies channel. In the extant version, no murder is even committed.
In September 1928, Warner Bros. Pictures purchased a majority interestin First National Pictures and from that point on, all "First National" productions were actually made under Warner Bros. control, even though the two companies continued to retain separate identities until the mid-1930's, after which time "A Warner Bros.-First National Picture" was often used.
The Library of Congress online catalogue lists the title of Helen Grace Carlisle's novel as "Mother Cry", but by all other accounts, the title is "Mother's Cry".
Vitaphone production reels #4559-4566 and #4530 (trailer)