The Johns Hopkins Medicine Board of Trustees has appointed a former federal prosecutor to lead its investigation into the Johns Hopkins All Children’s Hospital’s heart surgery unit, the health system announced late Tuesday.

F. Joseph Warin, of the global law firm Gibson Dunn, and his team will review the high mortality rates and other problems at the hospital’s Heart Institute and report back to a special committee of the board of trustees by May, the health system said.

Once the review is complete, the health system said it would also name an independent monitor at All Children’s to “make sure that the hospital is being held accountable for taking corrective action where necessary.”

The announcement was accompanied by a video of Johns Hopkins Health System president Kevin Sowers, who acknowledged for the first time that the hospital had been warned about problems by frontline workers.

“I know personally that many of you courageously spoke out when you had concerns but were ignored or turned away,” he said. “That behavior is unacceptable and will not be tolerated going forward.”

Sowers, who is also interim president at All Children’s, said he hoped to meet with the families of patients affected by problems in the Heart Institute in the coming days to share his “profound sadness for the failures of care they experienced.”

Rosana Escamilla, whose daughter Alexcia suffered a stroke after heart surgery in 2016, said she had “mixed emotions” about a potential meeting with Johns Hopkins executives.

“Part of me wants an explanation,” she said. “But what happened to Alexcia broke my heart and I don’t think an apology will fix that.”

The problems in the All Children’s heart surgery program were first made public by the Tampa Bay Times in late November. A Times investigation found that the mortality rate for heart surgery patients had tripled from 2015 to 2017, and was the highest for any heart surgery program in Florida over the past decade.

[ Read the investigation: Johns Hopkins promised to elevate All Children’s Heart Institute. Then patients started to die at an alarming rate. ]

The post-surgical infection rate spiked, the Times found. All Children’s surgeons made serious mistakes. Even less-complicated procedures went wrong in unusual ways.

The Times also reported that some Heart Institute employees brought concerns to their supervisors starting in 2015, but the hospital waited more than a year to stop performing complex surgeries.

After the report published, six senior officials left the hospital, including the CEO, three vice presidents and two surgeons who held leadership positions in the Heart Institute. A seventh official stepped down from his role as chairman of the surgery department, but remains employed at the hospital.

[ Read more: Top All Children’s executives resign following Times report on heart surgeries ]

[ Also: Three more All Children’s officials resign following Times investigation ]

Johns Hopkins previously announced plans to hire external experts to develop a plan to restart heart surgeries at All Children’s.

Warin, who will lead the independent review of the Heart Institute, is co-chairman of Gibson Dunn’s Investigations Practice Group and has represented nonprofit and for-profit hospitals in complex investigations, Johns Hopkins said.

According to the firm’s website, Warin has been hired to conduct investigations into allegations of wrongdoing in a wide variety of industries including energy, oil services, financial services, healthcare and telecommunications. His other areas of practice include white collar crime and regulatory and securities enforcement, including Foreign Corrupt Practices Act investigations.

Gibson Dunn also has experience conducting internal investigations for health systems “with issues regarding cardiac surgery practices,” Johns Hopkins said.

The Tuesday message reiterated plans to “share lessons learned from the review so that the Johns Hopkins Health System and other hospitals around the country can learn from the events at All Children’s.”

A spokeswoman has declined to say whether that would include making Warin’s full report available to the public.

[ Click here for all of the Times' coverage of Johns Hopkins and the All Children’s Heart Institute ]