Cassie, 28, died in hospital after being attacked at the store on January 13 and sustaining a throat injury.
Andrew Burke, 30, of Vincent Street, St Helens, appeared at Liverpool Crown Court via video link, BBC News reports.
His barrister David McLachlan QC, said there would be "no issue" that Cassie was unlawfully killed by Burke, but psychiatric reports are being prepared.
Judge David Aubrey QC adjourned the hearing until April 9, when Burke is expected to enter pleas.