Defense Secretary Ashton Carter said Friday that U.S. Navy boats may have entered Iranian waters due to a ‘navigation error,’ not a mechanical error as previously reported.

When the incident occurred on Tuesday, the U.S. Navy said that the ten captured sailors had accidentally drifted into foreign waters after becoming stranded. The boats were allegedly waiting for a rescue team from the USS Harry S. Truman. However, Carter is now suggesting that navigation error is to blame.

“The information that they have given us, and through their commanders is that they did stray accidentally into Iranian waters due to a navigation error,” Carter said at U.S. Southern Command in Miami. “So that seems to be the original cause of this, according to the interviews that we have done.”

On Tuesday, ten sailors were detained by the Iran Revolutionary Guard Corps for trespassing. They were held for a little under a day before being released to the U.S. Navy. However, Iran released video footage of the capture and a recording of one of the sailors apologizing for the entire incident. At the time, military officials and politicians alike didn’t understand why a sailor would apologize at all.

“When you have a problem with the boat, (do) you apologize the boat had a problem? No,” Vice President Joe Biden said in an interview with “CBS This Morning” on Wednesday. “And there was no looking for any apology. This was just standard nautical practice.”

Biden explained that rescuing stranded sailors was routine in the American military, and releasing captured sailors back to their original nations was routine and expected. There was thus nothing for the sailor to apologize for.

The revelation that the sailors may have genuinely wandered into Iranian territory put both videos in a new context.

The sailors are currently safe in Qatar.