It is hard to lose a loved one to death, harder yet to discover that a third party tampered with the loved one's last will and testament. When you have evidence sufficient to disprove or "break down" a will, make your case in probate court. The judge will hear the matter in trial and -- if you prove your allegations -- may invalidate the will.
A last testament is invalid if a requisite element is missing. All jurisdictions require a competent testator, defined by age and mental capacity. Most states require that a testator achieve a certain age -- generally 18 years old -- and be "of sound mind," meaning capable of rational thinking. Courts presume that adults are of sound mind, so anyone claiming otherwise must prove it by establishing that the testator was underage or irrational when he signed the will.
Disprove Free Will
Many will contests turn on issues of free will, so proof of either fraud or undue influence may invalidate affected will provisions. If someone tricks the testator into signing the will -- using deliberate lies to persuade her to change will provisions, for example -- it constitutes fraud. Forging the testator's name or switching wills at the last moment is also fraud. Undue influence happens if someone in a position of confidence with a fragile testator pressures her to alter the will.
Since a will only becomes effective upon the testator's death, the testator's signature is all-important. Probate codes prescribe methods of executing wills to ensure that the signature is in fact the testator's. All states require that at least two disinterested adults -- not heirs under the will -- watch the testator sign a printed will. Some states approve an unwitnessed will if it is written entirely in longhand by the testator. Proof of improper execution invalidates the will.
Hire an experienced attorney to file an objection in probate if you have evidence disproving an essential element of the will. Alternatively, review probate law and procedures, and draft an objection yourself. The court then sets a trial on the issues raised, at which time each side presents evidence. If you convince the judge that the will is invalid, an earlier will moves to probate or, if no earlier will exists, the estate passes to blood relatives under the laws of intestate succession.