Accounting period of purchase invoice

Dear members,

One client purchased goods on order & received purchased invoices dated 25.03.2012 (march month) in the month of April & May and goods also received in the month of april & may. There is no risk of goods in transit because seller charges insurance in the invoice. Now should it be account for in the month of March or April & May? Please tell the basis of accounting for the above transaction.

Thanks in advance