Mr. Kaman is right that in CA a motion for a new trial has to be filed before sentencing. However, the rules are not the same in all jurisdictions. In GA, for instance, a motion for new trial can be filed at any time if you can establish the extraordinary circumstances supporting the belated filing.
So out of curiosity I checked WA law and it appears that as a general rule you can make a collateral attack (motion for new trial, habeas, etc) within one year of the judgment becoming final. (pasted statute below) Moreover, there are a number of exceptions to the 1 yr limitation. (statute pasted below). Consult with a few experienced WA criminal defense attorneys. Most criminal defense attorneys will offer a free consultation.
§ 10.73.090. Collateral attack -- One year time limit
(1) No petition or motion for collateral attack on a judgment and sentence in a criminal case may be filed more than one year after the judgment becomes final if the judgment and sentence is valid on its face and was rendered by a court of competent jurisdiction.
(2) For the purposes of this section, "collateral attack" means any form of postconviction relief other than a direct appeal. "Collateral attack" includes, but is not limited to, a personal restraint petition, a habeas corpus petition, a motion to vacate judgment, a motion to withdraw guilty plea, a motion for a new trial, and a motion to arrest judgment.
(3) For the purposes of this section, a judgment becomes final on the last of the following dates:
(a) The date it is filed with the clerk of the trial court;
(b) The date that an appellate court issues its mandate disposing of a timely direct appeal from the conviction; or
(c) The date that the United States Supreme Court denies a timely petition for certiorari to review a decision affirming the conviction on direct appeal. The filing of a motion to reconsider denial of certiorari does not prevent a judgment from becoming final.
§ 10.73.100. Collateral attack -- When one year limit not applicable
The time limit specified in RCW 10.73.090 does not apply to a petition or motion that is based solely on one or more of the following grounds:
(1) Newly discovered evidence, if the defendant acted with reasonable diligence in discovering the evidence and filing the petition or motion;
(2) The statute that the defendant was convicted of violating was unconstitutional on its face or as applied to the defendant's conduct;
(3) The conviction was barred by double jeopardy under Amendment V of the United States Constitution or Article I, section 9 of the state Constitution;
(4) The defendant pled not guilty and the evidence introduced at trial was insufficient to support the conviction;
(5) The sentence imposed was in excess of the court's jurisdiction; or
(6) There has been a significant change in the law, whether substantive or procedural, which is material to the conviction, sentence, or other order entered in a criminal or civil proceeding instituted by the state or local government, and either the legislature has expressly provided that the change in the law is to be applied retroactively, or a court, in interpreting a change in the law that lacks express legislative intent regarding retroactive application, determines that sufficient reasons exist to require retroactive application of the changed legal standard.
You would need to file a Motion for a New Trial based upon the newly discovered evidence. In essence this evidence must be material and not merely cumulative, must be discovered after the trial and not reasonably discoverable prior to the orginal verdict, and must be of a nature as to probably have affected the jury's verdict. Check out the Court Rules that apply to this type of Motion in WA to determine the time limitations and applicability of this type of Motion to your case by consulting with an experienced WA defense lawyer as soon as possible. Good luck.
DISCLAIMER I do not practice law in your State. This answer is provided for informational purposes only. This answer does not constitute legal advice, create an attorney-client relationship, or constitute attorney advertising.
Motions for a New Trial have to be filed before sentencing. If you have been sentenced and later discovery exculpatory evidence you may have to file a writ of habeas corpus to bring this evidence to the Court's attention. Appeals are limited to what is already in the record.
As you note, the new evidence cannot be presented in an "appeal." Some form of collateral attack would have to be filed, such as a motion under Criminal Rule 7.8 or a Personal Restraint Petition. The rules for collateral attacks are quite complicated. It would be very difficult for your friend to handle that on his own. Unfortunately, he probably can't get a court appointed attorney for anything other than a direct appeal.
If your friend is in a position to hire an attorney, he should make sure it's someone with experience in Washington collateral attacks.