Matter of Gertsenshteyn, 24 I. & N. Dec. 111 (BIA 2007) (categorical approach to determining whether a criminal offense satisfies a particular ground of removal does not apply to the inquiry whether a violation of 18 U.S.C. 2422(a), interstate travel to engage in prostitution, was committed for "commercial advantage" and thus qualifies as an aggravated felony under INA 101(a)(43)(K)(ii), 8 U.S.C. 1101(a)(43)(K)(ii) (2000), where "commercial advantage" is not an element of the offense and the evidence relating to that issue is not ordinarily likely to be found in the record of conviction).
http://www.usdoj.gov/eoir/vll/intdec/vol24/3556.pdf