One by one, the celebrity Twitter accounts posted the same strange message: Send Bitcoin and they would send back double your money. Elon Musk. Bill Gates. Kanye West. Joseph R. Biden Jr. Former President Barack Obama. They, and dozens of others, were being hacked, and Twitter appeared powerless to stop it.

While some initially thought the hack was the work of professionals, it turns out the “mastermind” of one of the most high-profile hacks in recent years was a 17-year-old recent high school graduate from Florida, the authorities said on Friday.

Graham Ivan Clark was arrested in his Tampa apartment, where he lived by himself, early Friday, state officials said. He faces 30 felony charges in the hack, including fraud, and is being charged as an adult.

Two other people, Mason John Sheppard, 19, of the United Kingdom, and Nima Fazeli, 22, of Orlando, Fla., were accused of helping Mr. Clark during the takeover. Prosecutors said the two appeared to have aided the central figure in the attack, who went by the name Kirk. Documents released on Friday do not provide the real identity of Kirk, but they suggest that it was Mr. Clark.

Mr. Clark was skilled enough to go unnoticed inside Twitter’s network, said Andrew Warren, the Florida state attorney handling the case.

“This was not an ordinary 17-year-old,” Mr. Warren said.

Mr. Clark convinced one of the company’s employees that he was a co-worker in the technology department who needed the employee’s credentials to access the customer service portal, a criminal affidavit from Florida said. By the time the hackers were done, they had broken into 130 accounts and raised significant new questions about Twitter’s security.

Despite the hackers’ cleverness, their plan quickly fell apart, according to court documents. They left hints about their real identities and scrambled to hide the money they’d made once the hack became public. Their mistakes allowed law enforcement to quickly track them down.

Less than a week after the incident, federal agents, search warrant in hand, went to a home in Northern California, according to the documents. There, they interviewed another youngster who admitted participating in the scheme. The individual, who is not named in the documents because he or she is a minor, gave authorities information that helped them identify Mr. Sheppard and said that Mr. Sheppard had discussed turning himself in to law enforcement.

Because Mr. Clark is under 18, he was charged by the Florida state attorney in Tampa, rather than by federal authorities. His age also means that many details of his case are being kept under wraps.

One by one, the celebrity Twitter accounts posted the same strange message: Send Bitcoin and they would send back double your money. Elon Musk. Bill Gates. Kanye West. Joseph R. Biden Jr. Former President Barack Obama. They, and dozens of others, were being hacked, and Twitter appeared powerless to stop it.

While some initially thought the hack was the work of professionals, it turns out the “mastermind” of one of the most high-profile hacks in recent years was a 17-year-old recent high school graduate from Florida, the authorities said on Friday.

Graham Ivan Clark was arrested in his Tampa apartment, where he lived by himself, early Friday, state officials said. He faces 30 felony charges in the hack, including fraud, and is being charged as an adult.

Two other people, Mason John Sheppard, 19, of the United Kingdom, and Nima Fazeli, 22, of Orlando, Fla., were accused of helping Mr. Clark during the takeover. Prosecutors said the two appeared to have aided the central figure in the attack, who went by the name Kirk. Documents released on Friday do not provide the real identity of Kirk, but they suggest that it was Mr. Clark.

Mr. Clark was skilled enough to go unnoticed inside Twitter’s network, said Andrew Warren, the Florida state attorney handling the case.

“This was not an ordinary 17-year-old,” Mr. Warren said.

Mr. Clark convinced one of the company’s employees that he was a co-worker in the technology department who needed the employee’s credentials to access the customer service portal, a criminal affidavit from Florida said. By the time the hackers were done, they had broken into 130 accounts and raised significant new questions about Twitter’s security.

Despite the hackers’ cleverness, their plan quickly fell apart, according to court documents. They left hints about their real identities and scrambled to hide the money they’d made once the hack became public. Their mistakes allowed law enforcement to quickly track them down.

Less than a week after the incident, federal agents, search warrant in hand, went to a home in Northern California, according to the documents. There, they interviewed another youngster who admitted participating in the scheme. The individual, who is not named in the documents because he or she is a minor, gave authorities information that helped them identify Mr. Sheppard and said that Mr. Sheppard had discussed turning himself in to law enforcement.

Because Mr. Clark is under 18, he was charged by the Florida state attorney in Tampa, rather than by federal authorities. His age also means that many details of his case are being kept under wraps.