Conversely, if you are contemplating bringing a lawsuit based on defamation, the merit in your claim depends on existence of privilege(s) that might or might not attach to the circumstances and content of the speech.  Many reports to law enforcement agents are protected.

CALIFORNIA CODES
CODE OF CIVIL PROCEDURE
SECTION 44-48
 

44.  Defamation is effected by either of the following:
   (a) Libel.
   (b) Slander.



45.  Libel is a false and unprivileged publication by writing,
printing, picture, effigy, or other fixed representation to the eye,
which exposes any person to hatred, contempt, ridicule, or obloquy,
or which causes him to be shunned or avoided, or which has a tendency
to injure him in his occupation.



45a.  A libel which is defamatory of the plaintiff without the
necessity of explanatory matter, such as an inducement, innuendo or
other extrinsic fact, is said to be a libel on its face. Defamatory
language not libelous on its face is not actionable unless the
plaintiff alleges and proves that he has suffered special damage as a
proximate result thereof. Special damage is defined in Section 48a
of this code.



46.  Slander is a false and unprivileged publication, orally
uttered, and also communications by radio or any mechanical or other
means which:
   1. Charges any person with crime, or with having been indicted,
convicted, or punished for crime;
   2. Imputes in him the present existence of an infectious,
contagious, or loathsome disease;
   3. Tends directly to injure him in respect to his office,
profession, trade or business, either by imputing to him general
disqualification in those respects which the office or other
occupation peculiarly requires, or by imputing something with
reference to his office, profession, trade, or business that has a
natural tendency to lessen its profits;
   4. Imputes to him impotence or a want of chastity; or
   5. Which, by natural consequence, causes actual damage.




47.  A privileged publication or broadcast is one made:
   (a) In the proper discharge of an official duty.
   (b) In any (1) legislative proceeding, (2) judicial proceeding,
(3) in any other official proceeding authorized by law, or (4) in the
initiation or course of any other proceeding authorized by law and
reviewable pursuant to Chapter 2 (commencing with Section 1084) of
Title 1 of Part 3 of the Code of Civil Procedure, except as follows:
   (1) An allegation or averment contained in any pleading or
affidavit filed in an action for marital dissolution or legal
separation made of or concerning a person by or against whom no
affirmative relief is prayed in the action shall not be a privileged
publication or broadcast as to the person making the allegation or
averment within the meaning of this section unless the pleading is
verified or affidavit sworn to, and is made without malice, by one
having reasonable and probable cause for believing the truth of the
allegation or averment and unless the allegation or averment is
material and relevant to the issues in the action.
   (2) This subdivision does not make privileged any communication
made in furtherance of an act of intentional destruction or
alteration of physical evidence undertaken for the purpose of
depriving a party to litigation of the use of that evidence, whether
or not the content of the communication is the subject of a
subsequent publication or broadcast which is privileged pursuant to
this section. As used in this paragraph, "physical evidence" means
evidence specified in Section 250 of the Evidence Code or evidence
that is property of any type specified in Chapter 14 (commencing with
Section 2031.010) of Title 4 of Part 4 of the Code of Civil
Procedure.
   (3) This subdivision does not make privileged any communication
made in a judicial proceeding knowingly concealing the existence of
an insurance policy or policies.
   (4) A recorded lis pendens is not a privileged publication unless
it identifies an action previously filed with a court of competent
jurisdiction which affects the title or right of possession of real
property, as authorized or required by law.
   (c) In a communication, without malice, to a person interested
therein, (1) by one who is also interested, or (2) by one who stands
in such a relation to the person interested as to afford a reasonable
ground for supposing the motive for the communication to be
innocent, or (3) who is requested by the person interested to give
the information. This subdivision applies to and includes a
communication concerning the job performance or qualifications of an
applicant for employment, based upon credible evidence, made without
malice, by a current or former employer of the applicant to, and upon
request of, one whom the employer reasonably believes is a
prospective employer of the applicant. This subdivision authorizes a
current or former employer, or the employer's agent, to answer
whether or not the employer would rehire a current or former
employee. This subdivision shall not apply to a communication
concerning the speech or activities of an applicant for employment if
the speech or activities are constitutionally protected, or
otherwise protected by Section 527.3 of the Code of Civil Procedure
or any other provision of law.
   (d) (1) By a fair and true report in, or a communication to, a
public journal, of (A) a judicial, (B) legislative, or (C) other
public official proceeding, or (D) of anything said in the course
thereof, or (E) of a verified charge or complaint made by any person
to a public official, upon which complaint a warrant has been issued.
   (2) Nothing in paragraph (1) shall make privileged any
communication to a public journal that does any of the following:
   (A) Violates Rule 5-120 of the State Bar Rules of Professional
Conduct.
   (B) Breaches a court order.
   (C) Violates any requirement of confidentiality imposed by law.
   (e) By a fair and true report of (1) the proceedings of a public
meeting, if the meeting was lawfully convened for a lawful purpose
and open to the public, or (2) the publication of the matter
complained of was for the public benefit.



47.5.  Notwithstanding Section 47, a peace officer may bring an
action for defamation against an individual who has filed a complaint
with that officer's employing agency alleging misconduct, criminal
conduct, or incompetence, if that complaint is false, the complaint
was made with knowledge that it was false and that it was made with
spite, hatred, or ill will. Knowledge that the complaint was false
may be proved by a showing that the complainant had no reasonable
grounds to believe the statement was true and that the complainant
exhibited a reckless disregard for ascertaining the truth.



48.  In the case provided for in subdivision (c) of Section 47,
malice is not inferred from the communication.
 

*Current statutes as of April 8, 2010.