Abdur’Rahman v. Colson

(1) When is "cumulative error" a legally permitted basis for relief on federal habeas corpus; (2) is a prosecutor"s suppression of material exculpatory evidence excused whenever the defendant was aware of the facts contained therein, notwithstanding that the suppression prevented the defense from presenting the evidence of those facts to the jury; and (3) is defense counsel"s failure to investigate evidence that has some negative characteristics categorically immune from a claim of ineffective assistance of counsel?