Frank Zane shouldn’t be the standard which we use as a “cut off” to tell whether or not an athlete is natural. While he was on roids and fairly impressive, at 5’9, 185 lbs, 5% bodyfat, he only had an FFMI of around 26. While this is high, easily over the broscience “limit” of 25, several known natural bodybuilders in early bodybuilding history have surpassed it, with Jack Delinger hitting an FFMI over 28 in 1949 and George Eifferman hitting around in 1948. These and other high numbers were obtained before steroids were even available to the public, before Russians even gave steroids to their Olympic team. Likewise, these were before leg development was emphasized in bodybuilding to the degree it is now, so these people may have been able to attain higher levels of physical development than even then. Now, your current numbers list Lazar at 200 pounds at 5’9 and 5% bodyfat. This would put him at an FFMI of around 28, which is hard to achieve, but believable because of the above examples. However, other sources, such as SimplyShredded and HealthyCeleb put him at 5’11” and 195 lbs, which at a bodyfat percentage of 5%, would put him at an FFMI of – which is well under previous natural achievements. At the end of the day, he may be natural, even though it is way easier for him to be where he is with the help of steroids.
Unfortunately there exists no test that can determine a bodybuilder's detailed drug use in the far past, and doping test results are very easy to manipulate . Therefore, if you really want to know whether a bodybuilder is true natural, or which drugs he has been using to build his physique, you will have to ask him. The standard answer to this question is, however, always "No, I have never used any drugs". However, if you get to know the guy better, develop some friendship, give him some complements on his physique, and especially if he thinks that you are a drug user yourself or interested in becoming one, he might well loosen up and start telling you at least part of his true story.