AUGUSTA, Maine — A key witness in the trial that convicted a Winthrop man of torching a topless coffee shop in Vassalboro attempted suicide Thursday at the Kennebec County Jail.

Thomas J. Mulkern, 26, of Gardiner was taken to MaineGeneral Medical Center after he tried to strangle himself with a twisted bedsheet, Kennebec County Sheriff Randall Liberty said Thursday.

The sheriff described Mulkern as responsive and alert on his way to the hospital shortly after 11 a.m. when he was discovered in his cell. Mulkern was expected to be returned to the jail Thursday night.

Mulkern was arrested Tuesday and charged with the theft of money from a home and refusing to submit to arrest. He was arrested wearing hospital scrubs because he had been admitted to a hospital the previous night on suspicion of being under the influence of bath salts.

Officers needed to use a stun gun to subdue Mulkern, who was combative during his arrest, Liberty said.

Two weeks ago, Mulkern was released from the Kennebec County Jail after participating in a drug treatment program there.

“He has had a long struggle with substance abuse,” the sheriff said. “He was a speaker two weeks ago at the graduation. We’ll continue to work with him again on that.”

Mulkern was a key prosecution witness during the two-week trial of Raymond J. Bellavance Jr., 50, of Winthrop. Bellavance was convicted Dec. 30 of arson in the June 3, 2009, coffee shop fire.

On the eve of his graduation from the drug program, Mulkern, who was scheduled to testify for Bellavance, called Alan Kelley, deputy district attorney for Kennebec County, and changed his story. Mulkern told the jury on Dec. 23 that he saw Bellavance slosh gasoline on the coffee shop and set it ablaze.

BDN writer Judy Harrison and The Associated Press contributed to this report.