Pirelli suspects the two tyre failures at Sunday's Azerbaijan Grand Prix were caused by debris, but was not willing to draw a firm conclusion until a full investigation has taken place at its base in Milan this week.
Both Lance Stroll and Max Verstappen walked away from two separate 200mph accidents caused by left rear tyre failure on their cars.
Verstappen's accident resulted in the race being suspended with two laps remaining, setting up a sprint to the finish won by Sergio Perez.
The similarities of the two accidents raised questions over the reason for the failures, but a cut found on the left rear tyre from Lewis Hamilton's car could provide the answer.
The cut on Hamilton's tyre was not deep enough to result in a failure, but suggests debris somewhere on the track damaged the tyres on the cars of Stroll and Verstappen.
Pirelli also ruled out the possibility that the tyre failed due to excessive wear as neither of the tyres from the cars involved had unusually low tread depth at the point of failure.
"I believe I can exclude that failures were due to tyre wear, because it is not a matter of tyre wear," Pirelli motorsport director Mario Isola said.
"We found a cut on the inside shoulder of the rear left tyre used by Hamilton in the same stint.
"The cut was quite deep and big -- probably 6-7 cm -- but not cutting the construction, so the tyre was still in one piece.
"Just the tread is cut [on Hamilton's tyre], and when there was the red flag and Lewis came to the pit lane and changed the tyres we were able to find the cut.
"The left rear is not the most stressed in Baku, as talking about the tyres it is obviously rear right [that is most stressed].
"This is the preliminary investigation."
Isola said the debris theory was backed up by the nature of the failures, which happened suddenly and with no warning from tyre pressure sensors on the cars.
"There was no sign, or any warning, according to the teams," he added. "We have to receive the telemetry from them, but they told me there was no warning, no vibration, nothing to think there could be something in the tyres.
"Consider that the tyres fitted on the cars that crashed were back in the garage and in our fitting area just minutes ago, we need a bit of time to analyse them -- I don't want to give any preliminary conclusion.
"But it seems it is a cut due to debris. It is not a more-stressed tyre and we have evidence of another cut in the same position [on Hamilton's tyre].
"Both the accidents happened on more or less the same part of the circuit and a few laps difference, so we have other cars with the same number of laps, same tyres, without any issues.
"So the preliminary investigation is that it is probably due to an external factor or debris, kerb, or whatever, but I don't want to jump to a conclusion now as the plan now is to make a thorough investigation and make a report to the teams and the FIA that will be hopefully before Paul Ricard.
"Obviously it is a priority."