In 1936 and 1937 he represented the abortion care provider Isabel Annie Aves, who was tried four times for 'using an instrument with the intent to procure a miscarriage.' Neither the first trial in Napier in August 1936 nor the retrials in Wellington in October 1936,[7] December 1936 and February 1937 resulted in the jury reaching a verdict.[8][9][10] Harker's defence rested on lack of direct evidence; none of the women were gave evidence and the crown prosecutor relied on circumstantial evidence. In 1938 he also defended Colin Herbert Hercock who shot Aves after her return to the Hawkes Bay, getting him convicted of the lesser charge of manslaughter rather than murder[11] and subsequently getting his prison term reduced.[12]