I am considering recording a conversation or try to secretly record one between me and a non-federal employee. I am currently a federal employee, not FBI or CIA but am investigating on my own a possible cover-up which I am a victim and witness of. I want to know if I can do it legally without the others' consent.
California requires the consent of both parties. The relevant law is California Penal Code Section 632. However, take note of section e:
This section does not apply (1) to any public utility engaged in the business of providing communications services and facilities, or to the officers, employees or agents thereof, where the acts otherwise prohibited by this section are for the purpose of construction, maintenance, conduct or operation of the services and facilities of the public utility, or (2) to the use of any instrument, equipment, facility, or service furnished and used pursuant to the tariffs of a public utility, or (3) to any telephonic communication system used for communication exclusively within a state, county, city and county, or city correctional facility.
You also might find it allowable under section c on the grounds that communication is not considered confidential, but I doubt it based on the description you've given:
The term “confidential communication” includes any communication carried on in circumstances as may reasonably indicate that any party to the communication desires it to be confined to the parties thereto, but excludes a communication made in a public gathering or in any legislative, judicial, executive or administrative proceeding open to the public, or in any other circumstance in which the parties to the communication may reasonably expect that the communication may be overheard or recorded.
As to whether your situation would fall under that exempt category, it would depend on the specifics, and you probably should consult a lawyer. If you choose to record a conversation, you may have to defend yourself in court, and you may find that the recording is inadmissible in any actions against the alleged wrongdoer(s).