"Apparenza di buon diritto" in Italian, meaning that even though there might not be definite proof that a claim exists/right is being infringed etc., it is presumed to.

If the context is that of evaluating evidence in favor a seizure, you could use "probable cause"; otherwise, you could use something like my second suggestion.

PROBABLE CAUSE - A reasonable belief that a person has committed a crime. The test the court of appeals employs to determine whether probable cause existed for purposes of arrest is whether facts and circumstances within the officer's knowledge are sufficient to warrant a prudent person to believe a suspect has committed, is committing, or is about to commit a crime. U.S. v. Puerta, 982 F.2d 1297, 1300 (9th Cir. 1992). In terms of seizure of items, probable cause merely requires that the facts available to the officer warrants a "man of reasonable caution" to conclude that certain items may be contraband or stolen property or useful as evidence of a crime. U.S. v. Dunn, 946 F.2d 615, 619 (9th Cir. 1991), cert. Denied, 112 S. Ct. 401 (1992).