Opinion of the Court
GIERKE, Judge:A general court-martial composed of officer and enlisted members at Norton Air Force Base, California, convicted appellant, contrary to his pleas, of wrongfully using methamphetamine, in violation of Article 112a, Uniform Code of Military Justice, 10 USC § 912a. The adjudged and approved sentence provides for a bad-conduct discharge, confinement for 4 months, and reduction to the lowest enlisted grade. The Court of Criminal Appeals affirmed the findings and sentence. 42 MJ 753 (1995).
We granted review of the following issues:
I
WHETHER THE MILITARY JUDGE ERRED WHEN HE DENIED APPELLANT’S MOTION TO SUPPRESS THE RESULTS OF APPELLANT’S URINAL*120YSIS IN THAT THE PROSECUTION FAILED TO SHOW BY CLEAR AND CONVINCING EVIDENCE THAT THE RESULTS WERE ADMISSIBLE AS THE FRUITS OF A VALID INSPECTION WHEN THE EVIDENCE CLEARLY SHOWED THAT THE PURPOSE OF THE INSPECTION WAS TO OBTAIN EVIDENCE IN A CRIMINAL INVESTIGATION.
II
WHETHER THE MILITARY JUDGE ABUSED HIS DISCRETION WHEN HE GRANTED THE PROSECUTION’S MOTION TO EXCLUDE ANY EVIDENCE OF A PREVIOUS, RECENT ATTEMPT OF AN UNKNOWN PERSON TO PLANT DRUGS ON AN OFFICER WHO WORKED IN THE SAME BUILDING AS APPELLANT.
We resolve both issues against appellant.
Special Agent (SA) John Bornt of the Air Force Office of Special Investigations (OSI) testified that on August 28,1992, he received an anonymous telephone call. The caller said that Major (Maj) Adams, Chief of the Consolidated Base Personnel Office (CBPO), was involved in a sale of marijuana in the CBPO parking lot. On September 4, Maj Adams discovered marijuana in her briefcase. She apparently reported it to the OSI. The OSI interviewed Maj Adams, offered her a polygraph examination, and thereafter cleared her of any wrongdoing. The OSI concluded that someone probably had placed the marijuana in Maj Adams’ briefcase while it was in her office. SA Bornt testified that they looked at who had access and motivation to put marijuana in Maj Adams’ briefcase. They interviewed a group selected at random by one of the officers at CBPO. Three persons were targeted based on “the best motivation and best access” to Maj Adams’ briefcase. Appellant was not one of those targeted.
SA Bornt testified that he briefed Maj Stringfield, deputy staff judge advocate and chief of military justice at Norton AFB. She asked SA Bornt what he thought about the “potential benefits” of conducting a urinalysis. At the time, thinking she was referring to the entire unit rather than just CBPO, SA Bornt responded that “it sounds like a good idea.” He testified, however, that he did not think it would help OSI find out who had attempted to frame Maj Adams, but he thought that the Adams incident might indicate some drug problems in the unit.
SA Bornt testified that he did not brief the squadron commander, Maj Kera, or the acting group commander, Lieutenant Colonel (LtCol) Schell, about the benefits of a urinalysis. After Maj Stringfield told him she would approach command about it, he “was basically out of it.”
LtCol Schell testified that he ordered the urinalysis of all military personnel in Building 505 (the location of CBPO). Col Underwood, commander of the 63d Support Group, was absent, and LtCol Schell had assumed command in his absence. In his written order, LtCol Schell ordered that “all military personnel assigned to duty in building 505, Norton AFB ... provide urine samples” to be tested for “illegal drugs.” He further ordered that those who were on leave, temporary duty, or sick in quarters “shall provide a urine sample for testing on the first duty day after returning to duty.”
LtCol Schell testified that the incident involving Maj Adams caused him to accept the suggestion from “the Judge Advocate’s office” and order the urinalysis. He testified that there was “a lot of finger pointing, hard feelings,” and “tension” in Building 505 as a result of the Adams incident. LtCol Schell “wanted to get people either cleared or not cleared.”
LtCol Schell testified that no particular person was targeted for investigation so far as he knew. LtCol Schell also ordered a sweep of Building 505 by drug detection dogs. The drug dogs swept the building before the urinalysis but detected nothing.
Col Underwood testified that he participated in “discussions way before that urinalysis took place.” He testified that “the thing that we thought is that there may be a high degree of probability that the person who planted the marijuana could have also been *121using it — or an illicit drug of some sort.” He testified that “[t]here were morale problems in the unit,” but “[t]he morale problems were not the reason for the urinalysis.” Col Underwood testified that he was absent from his command on leave from September 8 through 16 and from September 19 through 26. He remembered “discussing options” but not making any decisions before departing on leave. The decision to order the urinalysis was made in his absence, and the plans were finalized by LtCol Schell while he was in command.
The urinalysis originally was scheduled for Friday, September 18. It was moved to Monday, September 21, “because Col Hopper, the Wing Commander, generally believed that drug use was more prevalent on weekends,” so a urinalysis on a Monday would be more effective in detecting drug use. Although LtCol Schell ordered the urinalysis, he testified that the change of date from September 18 to September 21 was “not my decision.”
According to a stipulation of fact, Senior Master Sergeant Whittington, the Mission Support Squadron (MSSQ) First Sergeant, acknowledged that a number of unit members did not appear for the urinalysis, but no action was taken to test them. The absent members were not excused; “it was just an administrative error.” Fifty-nine of the 79 members of appellant’s unit were tested. Only appellant tested positive for any drug.
At trial, defense counsel moved to suppress the fruits of the urinalysis on the ground that the purported inspection was a subterfuge for an illegal search. The military judge denied the motion. In his findings of fact and conclusions of law, he concluded that LtCol Schell’s “primary purpose was to resolve the questions raised by the Adams incident, not to prosecute someone.” Although the military judge labeled it as a conclusion of law, the court below treated his “conclusion” concerning LtCol ScheU’s “primary purpose” as a finding of fact. 42 MJ at 755. We agree with this characterization. See United States v. Gardner, 41 MJ 189,191 (CMA 1994) (“military judge’s finding regarding the ‘primary purpose’ is a matter of fact”).
Appellant’s defense was based on innocent ingestion. Defense counsel wanted to ask SA Bomt about the effort to frame Maj Adams on the theory that if someone planted marijuana in Maj Adams’ briefcase, “somebody else may have planted methamphetamine in Sergeant Shover’s coffee.” Trial counsel moved in limine to suppress any reference to the Adams incident on the ground that it was irrelevant. The military judge granted trial counsel’s motion in limine. He explained:
It takes a fairly large leap to conclude from Major Adams’ [unknowing] possession of marijuana something about Sergeant Shover’s alleged use of methamphetamine — different person, different drug — if planted in both eases, a different way. I mean, one to show possession and one to show use. Even if you conclude that there’s some minimal relevance of that, I am persuaded that the likelihood of confusion of what the issues are before this court and the waste of time are not worth it under Rule 408.
Appellant testified in his own defense. He described his activities before the urinalysis and denied experiencing anything that would indicate use of methamphetamines. When trial counsel asked him if he thought he could get by with lying, appellant responded, “No, sir. I’m innocent, and I’m gonna stick to that.”
The military judge instructed the members that “[t]he evidence has raised the issue of ignorance in relation to wrongful use of methamphetamine.” He instructed the members that appellant could not be convicted “[i]f he was, in fact, ignorant of the fact that he was ingesting a controlled substance.” He also told them that the defense would “not exist” if the members “were satisfied beyond a reasonable doubt that the accused was not ignorant” as he claimed.
Motion to Suppress Urinalysis Evidence (Issue I)
Appellant argues that the military judge erred because the prosecution faded to *122show by clear and convincing evidence that the urinalysis was a valid inspection. The Government argues that the prosecution met its burden.
The parties agree that the urinalysis evidence is governed by Mil.R.Evid. 313, Manual for Courts-Martial, United States (1995 ed.). It defines an inspection as “an examination of the whole or part of a unit, organization, installation, vessel, aircraft, or vehicle, ... conducted as an incident of command the primary purpose of which is to determine and to ensure the security, military fitness, or good order and discipline of the unit, organization, installation, vessel, aircraft, or vehicle. An inspection may include ... an examination to locate and confiscate unlawful weapons and other contraband.” On the other hand, the rule provides that “[a]n examination made for the primary purpose of obtaining evidence for use in a trial by court-martial or other disciplinary proceedings is not an inspection within the meaning of this rule.” The rule further provides that “the prosecution must prove by clear and convincing evidence that the examination was an inspection” where “a purpose ... is to locate weapons or contraband, and if ... the examination was directed immediately following a report of a specific offense in the unit, ... and was not previously scheduled!.]”
In United States v. Gardner, 41 MJ at 191, we held that “the military judge’s finding regarding the ‘primary purpose’ is a matter of fact,” and “the issue of whether the examination is an inspection is a matter of law that this Court will review de novo.” A military judge’s preliminary finding of fact will not be overturned unless clearly erroneous, but his rulings on questions of law are reviewed de novo. See United States v. Sullivan, 42 MJ 360, 363 (1995) (factfinding reviewed “under the clearly erroneous standard and conclusions of law under the de novo standard”).
Because the urinalysis “was directed immediately following a report” that an unknown person had planted marijuana in Maj Adams’ briefcase, the burden was on the prosecution to “prove by clear and convincing evidence” that the urinalysis was an inspection within the meaning of Mil.R.Evid. 313. In deciding whether a urinalysis is a valid inspection or a subterfuge search, the focus is on the commander who ordered the urinalysis. United States v. Taylor, 41 MJ 168, 172 (CMA 1994). Thus, we focus on Lt Col Schell, who was in command at the time in question, and who planned and ordered the urinalysis. He testified unequivocally that his purpose was to end the “finger pointing, hard feelings,” and “tension” in the unit and “get people either cleared or not cleared.” He testified that no particular person was targeted. Based on his testimony, we hold that the military judge’s finding of fact concerning the primary purpose of the urinalysis was supported by the evidence and therefore not “clearly erroneous.”
Turning to the legal question whether the urinalysis was an “inspection” instead of a search, we hold that the military judge correctly applied the standards set out in Mil. R.Evid. 313 and the decisions of this Court. Accordingly, the military judge did not abuse his discretion by admitting the urinalysis evidence.
Evidence of Attempted Frame-up (Issue II)
Appellant contends that the military judge abused his discretion by excluding evidence of the attempt to frame Maj Adams because the evidence was relevant to his claim of innocent ingestion. The Government disagrees.
Mil.R.Evid. 403 empowers a military judge to exclude relevant evidence “if its probative value is substantially outweighed by the danger of unfair prejudice, confusion of the issues, or misleading the members, or by considerations of undue delay, waste of time, or needless presentation of cumulative evidence.” The proponent of the evidence has the burden of showing admissibility. See S. Saltzburg, L. Sehinasi & D. Schlueter, Military Rules of Evidence Manual 422 (3d ed.1991), citing Mil.R.Evid. 103. When a military judge exercises discretion under Mil. R.Evid. 403 and excludes evidence, “appellant has the burden of going forward with conclusive argument that the judge abused *123Ms discretion.” United States v. Mukes, 18 MJ 358 (CMA 1984).
We hold that the military judge did not abuse Ms discretion. We agree with the military judge that the two incidents were too dissimilar. Maj Adams was a supervisor; appellant was not. The Adams meident involved marijuana; appellant’s case involved methamphetamines. The Adams incident mvolved allegations of possession and sale; appellant was charged with use. Fmally, we agree with the observation of the court below that appellant’s speculative theory that someone “spiked” Ms coffee at work is undermined by the fact that no one else m the uMt who had access to the coffee tested positive for drugs. 42 MJ at 757.
Decision
The decision of the Urnted States Air Force Court of Criminal Appeals is affirmed.
CMef Judge COX and Judge CRAWFORD concur.