Although once a petition is filed, general civil discovery mechanisms may be utilized, there is a possible alternative that does not require an initial probate filing. Probate Code §§8870-8873 provide special discovery procedures for use when a person is believed to have wrongfully possessed or concealed the decedent's property, or to have knowledge or possession of a lost will or of certain evidence regarding the decedent's assets. The personal representative or other interested party may petition the court for an order that a citation be issued compelling the person to answer interrogatories or appear before the court for examination under oath, or both. The interrogatories or examination may concern any of the following allegations (Prob C §8870(a)):
The person has wrongfully taken, concealed, or disposed of estate property; or
The person has knowledge or possession of any of the following:
A deed, conveyance, bond, contract, or other writing that contains evidence of or tends to disclose the decedent's right, title, interest, or claim to property;
A claim of the decedent; or
A lost will of the decedent.
Disobedience of the citation may be punished as contempt of court. Prob C §8870(c).
NOTE: Probate Code §859 imposes liability for double damages on a person who wrongfully takes, conceals, or disposes of estate property.
If not the petitioner, the representative must receive notice of these discovery proceedings, as must persons who have filed requests for special notice. Prob C §8870(d). See Prob C §§1220 (notice to representative), 1250 (request for special notice), 1252 (notice to person requesting special notice).
On petition by the representative, the court may also issue a citation to a person who has possession or control of property in the decedent's estate to appear before the court and account under oath for the property and the person's actions with respect to the property. Prob C §8873(a). Disobedience of a citation under §8873 may be punished as contempt of court. Prob C §8873(b).
The information you obtain at this site is not, nor is it intended to be, legal advice. You should consult an attorney for individual advice regarding your own situation.
You need to file a suit against the trustee for an accounting. As part of the suit you can take the deposition of the beneficiary and anyone else with knowledge of the assets.
The response given is not intended to create, nor does it create an ongoing duty to respond to questions. The response does not form an attorney-client relationship, nor is it intended to be anything other than the educated opinion of the author. It should not be relied upon as legal advice. The response given is based upon the limited facts provided by the person asking the question. To the extent additional or different facts exist, the response might possibly change. Attorney is licensed to practice law only in the State of California. Responses are based solely on California law unless stated otherwise.
You have not identified your position although it sounds like you may be the Trustee. If you are the Trustee you can utilize procedures in the probate court to subpoena records of the 3rd party and the beneficiary as well as take their depositions. In any event you will need to hire a lawyer to assist you. The lawyer can advise you whether you should be seeking some extraordinary procedures (protective orders, etc.) out the outset of the litigation or whether the more leisurely pace of probate law and motion practice is suffcient.
This is a general answer only and you should seek the advice of counsel to address facts specific to your circumstances.