TALLAHASSEE, Fla. -- Florida Department of Law Enforcement Commissioner Guy Tunnell resigned Thursday amid criticism that he mishandled an investigation into the death of a teenager at a Panama City boot camp.

Gov. Jeb Bush accepted the resignation, but did not offer an explanation for it.

"I thank Guy for his service. He is a dedicated law enforcement officer who leaves behind an agency that is second to none," Bush said in a statement.

Messages left on Tunnell's cell phone were not immediately returned as were messages left after hours for Bush's representatives.

Rep. Dick Kravitz, R-Orange Park and chair of the House Criminal Justice Committee, said the governor's office called to tell him that about the resignation, but wouldn't tell him why Tunnell resigned. He was only told that Tunnell went to the governor's mansion to turn it in.

"I'm sort of in the dark as to the reason," Kravitz said. "I was just sort of surprised."

Bush appointed then-Bay County Sheriff Tunnell as the head of the FDLE in August 2003.

As sheriff, Tunnell started the Panama City juvenile boot camp where a 14-year-old boy's January altercation with guards was caught on security videotape. The teen, Martin Lee Anderson, died a day after being kicked and kneed by guards. The boot camp has been closed.

Tunnell has recently been criticized for the handling of the investigation into Anderson's death.

Sen. Tony Hill, D-Jacksonville, one of several black lawmakers who have questioned the investigation, said FDLE's failure to ask Anderson's family about his medical history was among the signs the investigation wasn't being handled properly.

Tunnell's resignation "was the appropriate decision and I think it was appropriate for the governor to accept the resignation," said Hill.

Bush had said Tunnell should not have communicated with Bay County Sheriff Frank McKeithen during the state's investigation, after Tunnell forward e-mails to the sheriff that criticized those who questioned the effectiveness off the boot camp concept.

Sen. Stephen Wise, R-Jacksonville, who was among the lawmakers mentioned in the e-mails, said Tunnell called him to offer to let him watch the video. Wise said he told Tunnell that he didn't need to see them to know something wrong happened and that he could wait to read the investigation's reports.

Wise speculated that the recent pressure may have affected Tunnell's decision.

"It's a stressful job," Wise said. "I know the family issue really bothered him. When you're in the public light, it always affects the family the worst, and when the family is involved in something it really becomes stressful."

Tunnell has said that remaining neutral in the investigation was difficult.

"I am a Bay County native and I'm proud of it, but I think FDLE's reputation (of) being straightforward, professional and calling it like it is, is well known," he said last month. "I don't see any tarnish."

He also said it was easy for people to "throw stones when they really don't have an idea of what they're talking about."

Anderson collapsed while doing exercises during his first day at the camp. The Bay County sheriff's office has said the guards were trying to get him to participate after he became uncooperative.

An initial autopsy found the boy died from complications of sickle cell trait, a usually benign blood disorder -- but a nationally known pathologist, Dr. Michael Baden, said after observing a second autopsy that Anderson likely was suffocated during the confrontation at the camp. Results of the second autopsy haven't been completed.

Last month, Tunnell's 31-year-old son Bradley resigned from the state Department of Corrections after being demoted his role in a brawl while in Jacksonville for a softball tournament in May.

Tunnell's tenure as sheriff was not without controversy. A Panama City nightclub sued him in 2001, accusing him of false prosecution after the club's two owners were acquitted on drug-related charges. The lawsuit was later dropped with the owners joined Tunnell in working on club security matters.

Tunnell also in 2001 defended his hiring of a convicted scam artist as a receptionist, saying the ex-convict deserved a second chance, was an excellent employee and did only clerical work.