Evidence sample analysis
MBE Evidence Prior Bad Acts: MIMIC 404(b) Trap
Review a fresh FRE 404(b) prior-bad-acts hypo with examiner-style analysis on non-propensity admissibility, MIMIC purposes, and limiting instructions.
Fact pattern
Daria is on trial for the armed robbery of the Westwood Credit Union on March 4. The robber wore a yellow ski mask, used a chrome revolver with a wooden grip, and forced the teller to hand over cash in a cloth bag stamped with a faded paw-print logo. The prosecution offers evidence that, two years earlier, Daria pleaded guilty to robbing a different credit union in another county. In that earlier robbery, the robber wore a yellow ski mask, used a chrome revolver with a wooden grip, and used a cloth bag stamped with the same faded paw-print logo. Daria objects under FRE 404(b), arguing the prior robbery is inadmissible character evidence. The prosecution responds that the prior act is offered to show identity, not propensity.
Quick answer
The court should admit the prior robbery for the limited purpose of proving identity, give a limiting instruction on request, and bar the jury from using the prior act as propensity evidence. Under FRE 404(b)(1), evidence of a prior crime, wrong, or other act is not admissible to prove a person's character in order to show that on a particular occasion the person acted in accordance with the character. Under FRE 404(b)(2), the same evidence may be admissible for non-propensity purposes — commonly summarized by the MIMIC mnemonic: motive, intent, mistake (absence of), identity, and common plan or scheme. To use prior-act evidence for identity, the proponent must show a sufficiently distinctive modus operandi — a signature so unusual that it acts as a fingerprint linking the two acts. The proponent must also satisfy FRE 403 balancing and, on request, the court must give a limiting instruction under FRE 105.
IRAC model answer
May the prosecution introduce Daria's prior credit-union robbery to prove that she is the robber of the Westwood Credit Union, even though it would be excluded as propensity evidence?
Under FRE 404(b)(1), evidence of a prior crime, wrong, or other act is not admissible to prove a person's character in order to show that on a particular occasion the person acted in accordance with the character. Under FRE 404(b)(2), the same evidence may be admissible for non-propensity purposes — commonly summarized by the MIMIC mnemonic: motive, intent, mistake (absence of), identity, and common plan or scheme. To use prior-act evidence for identity, the proponent must show a sufficiently distinctive modus operandi — a signature so unusual that it acts as a fingerprint linking the two acts. The proponent must also satisfy FRE 403 balancing and, on request, the court must give a limiting instruction under FRE 105.
The prosecution offers the prior robbery to prove identity, not to argue that Daria is a habitual robber. The two crimes share an unusually specific signature: the same yellow ski mask, the same chrome revolver with a wooden grip, and a cloth bag stamped with the same faded paw-print logo. None of those features individually would be especially distinctive — yellow ski masks are not unique — but in combination, and especially with the paw-print bag, the cluster forms a signature that is highly probative of identity. The probative value is substantial; the prejudicial effect of jurors thinking Daria is a "robber type" is real but can be mitigated by a limiting instruction telling the jury to consider the prior act only on identity, not on character. Under FRE 403 balancing, the probative value of the modus-operandi match outweighs the unfair prejudice. Daria is entitled to a limiting instruction under FRE 105 if she requests one.
The court should admit the prior robbery for the limited purpose of proving identity, give a limiting instruction on request, and bar the jury from using the prior act as propensity evidence.
Numbered reasoning steps
- Identify the proponent's purpose — propensity (barred under 404(b)(1)) or one of the MIMIC purposes (allowed under 404(b)(2))?
- For identity, evaluate whether the modus operandi is distinctive enough to function as a signature.
- Run FRE 403 balancing — probative value vs unfair prejudice, confusion, or waste of time.
- Address any required notice under FRE 404(b)(3) for criminal cases.
- On request, provide a FRE 105 limiting instruction restricting the jury's use of the evidence.
Why wrong answers fail
Propensity is the precise inference FRE 404(b)(1) prohibits. Admissibility must rest on a non-propensity purpose like identity.
FRE 404(b)(2) allows prior acts for MIMIC purposes — motive, intent, absence of mistake, identity, and common plan or scheme.
That confuses 404(b) with 608/609 impeachment rules. Identity evidence under 404(b)(2) is admissible in the case-in-chief without a credibility predicate.
FRE 404(b)(3) requires reasonable notice in criminal cases, but the rule does not impose a fixed 14-day floor — the deadline turns on the court's scheduling order.
Issue-spotting checklist
- Pin down the proponent's articulated purpose before debating admissibility.
- For identity, look for a distinctive cluster of details — a single common feature is rarely enough.
- Run FRE 403 balancing explicitly; do not assume probative value automatically wins.
- Confirm the criminal-case notice obligation under FRE 404(b)(3).
- Request a FRE 105 limiting instruction to confine the jury's use to the proper purpose.
Primary law and source anchors
- Federal Rule of Evidence 404(b) Prior-act evidence inadmissible for propensity, admissible for non-propensity purposes (MIMIC).
- Federal Rule of Evidence 403 Balancing of probative value against unfair prejudice and other countervailing concerns.
- Federal Rule of Evidence 105 Court must give a limiting instruction on request when evidence is admissible for one purpose but not another.
- Huddleston v. United States, 485 U.S. 681 (1988) No preliminary finding of conditional fact is required; the jury must be able to find the prior act by a preponderance.