Walid Muhammad Salih bin Mubarak bin Attash (Arabic: وليد محمد صالح بن مبارك بن عتش; born 1978)[7] is a Yemeni prisoner held at the United States' Guantanamo Bay detention camp under terrorism-related charges and is suspected of playing a key role in the early stages of the 9/11 attacks.

[16][17] Hailing from a prominent Saudi family on friendly terms with Osama bin Laden,[18] Attash had several brothers fighting during the tumultuous 1990s in Afghanistan.

[20] In late 1999, while using the nom de guerre Khallad, Attash phoned Khalid al-Mihdhar, informing him of the upcoming Kuala Lumpur al-Qaeda Summit.

While there, the FBI received a transcript of a phone call from Fahd al-Quso and one of the USS Cole bombers, which mentioned giving Attash $5,000 to purchase a new prosthesis.

[22] In the spring of 1999, Bin Laden selected four individuals to serve as suicide operatives after discussing what U.S. targets to crash planes into.

[4] Near the end of December 1999, KSM directed Bin Attash to conduct a casing mission in support of the Planes Operation.

[24] Upon his return to Karachi, Pakistan, Bin Attash prepared a written report and briefed KSM and Mohammed Atef (the military commander of al-Qaeda) on airline security and his ability to get the razor knife on board the flights.

It also said that authorities knew of an al-Qaeda cell dubbed "Father of the Leg" that revolved around a senior member, and believed this was a reference to Attash due to his missing limb.

The DoD was later to publish a ten-page transcript from the unclassified portion of the Tribunal: I was the link between Usama bin Laden and his deputy Sheikh Abu Hafs al-Masri and the cell chief in Nairobi.

I used to supply the cell with whatever documents they need from fake stamps to visas, whatever.His Personal Representative met with him on February 13, and told the tribunal that Attash confirmed that many of the allegations were basically correct, but that he had never owned a telephone and that he had forged the Yemeni registration card himself.

The US Department of Defense announced on 9 August 2007, that all fourteen of the "high-value detainees" who had been transferred to Guantanamo from the CIA's black sites, had been officially classified as "enemy combatants".

On 8 December 2008, Khalid Sheikh Mohammed told the judge that he and the other four indictees wished to confess and plead guilty; however, the plea would be delayed until after mental competency hearings for Hawsawi and bin al-Shibh.

[40] Two of the other Yemenis Saba News reported would face charges were: Ramzi bin al-Shibh and Abd al-Rahim al-Nashiri.

Reporting in late 2022 indicated that the Biden administration was weighing a possible plea deal with Bin 'Attash and the four other suspected terrorists' Military Commission Trial.

[42] On 31 July 2024, Attash agreed to plead guilty to avoid the death penalty,[14][15] however it was revoked by Defense Secretary Lloyd Austin two days later.