Reports say the masked man with a British accent who has featured in several Islamic State beheading videos has been identified.
The BBC reported on February 26 that the militant known as "Jihadi John" is Muhammad Emwazi, a Kuwaiti-born British man in his mid-twenties believed to be from West London, who was known to British security services.
The Washington Post newspaper said Emwazi was a Briton from a well-to-do family who graduated from college with a degree in computer programming.
The University of Westminster confirmed that a student of that name graduated in 2009.
British antiterrorism officials wouldn't confirm the man's identity, citing a "live counterterrorism investigation."
National Security Council spokeswoman Bernadette Meehan said the United States couldn't confirm or deny the identity, either.
White House Press Secretary Josh Earnest also declined to confirm the identity of the suspect.
Earnest said that investigators over the last several months "have found it to their advantage to not talk publicly about the details or progress of that investigation."
"Jihadi John" appeared in a video released in August showing the killing of American journalist James Foley.
Former IS prisoners identified him as one of a group of British militants that captives had nicknamed "The Beatles."
A man with similar stature and voice also featured in videos of the killings of American journalist Steven Sotloff, Britons David Haines and Alan Hemming and U.S. aid worker Abdul-Rahman Kassig.
The reports said Emwazi was known to Britain's intelligence services before he traveled to Syria in 2012.
CAGE, a London-based advocacy group that counsels Muslims in conflict with British intelligence services, said Emwazi first contacted the group in 2009.
According to CAGE, Emwazi said he had traveled to Tanzania after leaving university, but was deported and questioned in Amsterdam by British and Dutch intelligence services, who suspected him of attempting to join al-Shabaab militants in Somalia.
In 2010, Emwazi alleged that British intelligence services were preventing him from traveling to Kuwait, where he planned to work and marry.
CAGE quoted an email Emwazi had sent saying, "I had a job waiting for me and marriage to get started. But now I feel like a prisoner, only not in a cage, in London."