I'm not sure what you're implying that he could be "shaking down" Trump for, but I think Bukele already knows they imprison innocent people... it has been reported that they have released at least 8,000 of them in the last 3 years, which also seems to contradict the often cited claim that "nobody ever leaves" CECOT.
https://www.swissinfo.ch/spa/bukele-reconoce-8%2e000-inocent...