He is credited with the expansion of the collection of antiquities of the museum, but he was also involved in a number of controversies, including a tax manipulation scheme to buy artifacts of dubious provenance and purchase of a number of artifacts widely considered to be fake.
He returned to Czechoslovakia after World War II and obtained a doctorate from Charles University in Prague.
Subsequently, he was employed by the Greek and Roman art department of Charles University and taught there.
[3] During his tenure as curator, Frel considerably expanded the collection of Greek and Roman artifacts, transforming it to one of the leading museums of the world.
Before leaving the Getty Museum in 1986 he hired Marion True, the new curator, who was later charged with laundering stolen artifacts.