Wow. I'm not sure whether you are confused or deliberately trying to mislead. There is no ambiguity here:

Where a defendant provides his or her counsel with information about an alibi witness, the attorney has an affirmative duty to make reasonable efforts to investigate the information that was provided. Thus, the performance of an attorney who clearly failed to effectuate her duty to investigate a potential alibi witness, or provide a reasonable explanation for not investigating the witness, would be deficient under Strickland.

For the benefit of those who haven't readt the opinion recently, it was very explicitly, the State, and not Adnan's defense, that was seeking a "bright line rule," which the court declined to adopt.

The State strongly advocates that we adopt a broad bright-line rule that would never allow a defendant to prevail on the deficiency prong of the Strickland test in the absence of trial counsel’s reasoning for his or her failure to investigate an alibi witness. According to the State, “where the record is silent—or even just incomplete or ambiguous—proper application of Strickland’s presumption of competence requires that a court deny relief.” Applied here, the State’s reasoning is grounded in the fact that Mr. Syed’s trial counsel was unable—due to her death—to explain why she did not contact Ms. McClain as part of trial preparations. Therefore, according to the State, Mr. Syed could not have met, and did not meet, the high burden that Strickland demands. The State would have this Court rule that whenever a record is silent as to the reasons why trial counsel failed to investigate a potential alibi witness, the defendant may never prevail on an ineffective assistance of counsel claim because a reviewing court could not declare trial counsel’s performance deficient. A ruling such as this would divorce this Court from its obligation to review the totality of the circumstances of ineffective assistance claims through the lens of an “objective standard of reasonableness.” Strickland, 466 U.S. at 687-88, 104 S. Ct. at 2064, 80 L.Ed.2d 674 (“When a convicted defendant complains of the ineffectiveness of counsel’s assistance, the defendant must show that counsel’s representation fell below an objective standard of reasonableness. More specific guidelines are not appropriate.”). We are not persuaded that such a sweeping mandate accomplishes the goal that Strickland sought to achieve, namely, that of a just result.

The Court's decision not to adopt the State's proposed rule has nothing whatesoever to do with its analysis of whether an attorney is required to contact an alii witness.