Both have been granted name suppression to allow them time to inform families overseas in India.
Detectives investigating the homicide believe they have now found "a weapon of interest".
"Police thank those members of the public who contacted the Operation Bastille team about items they located which may have been of interest," a statement said.
Father-of-one Mr Singh, 35, was stabbed to death as he sat in his car beside wife Amandeep Kaur outside the Manukau Event Centre in Norman Spencer Drive, Papatoetoe, about 7.20pm on Thursday.
They were on their way home from work and had stopped to eat a takeaway meal when the attack occurred.
