a) Delay in lodging FIR is a fatal to the criminal case. There is a scope for concoction or adding coloured version. The Court should be very careful to act on such information stated in the FIR. If the reasons explained for delay and if it appears natural defect it can be consider.
No. Police do not do prior investigation before registration of FIR.
b) The Court suspects integrity of the Police if the facts suppressed in the F.I.R. The Court will see consider genuine FIR.
C) It can be used for corroboration by the Prosecution under Section 157 of Indian Evidence Act. For contradiction by the Accused under Section 145 I.E.A. It can also impeach the credit of maker under Section 155 I.E.A.