per se exclusionary rule

Only a per se exclusionary rule as to such testimony can be an effective sanction to assure that law enforcement authorities will respect the accused's constitutional right to the presence of his counsel at the critical lineup. In the absence of legislative regulations adequate to avoid the hazards to a fair trial which inhere in lineups as presently conducted, the desirability of deterring the constitutionally objectionable practice must prevail over the undesirability of excluding relevant evidence.