So what happened around 1990/91? You had the first Gulf war, and given that Iraq was a sworn enemy of Iran, suddenly the Iran track went cold. Also, in 1991 Bush Sr and James Baker organized a “peace” conference in Madrid - Syria was part of the Arab delegation, and it would have been very bad for the negotiators if one of the leading Arab nations had been tied to the Lockerbie atrocity. The Madrid Conference ended 1 November 1991, and the Libyans were indicted 13 November 1991. From then on the Syrian track was demoted to the conspiracy pages.
Libya may well have been guilty, but when political imperatives and results of criminal investigations suddenly run in parallel there are always reason to be suspicious.
https://observer.com/2018/12/bomb-pan-am-103-lockerbie-iran-remains-a-30-year-mystery/
Guess who was the US investigator at the time? Robert Mueller of Russiagate.
Qadaffi owed Iran a big favor