Confessed killer Mark W. Hofmann's Sept. 15 drug overdose was an attempt to take his own life, prison investigators have concluded.

Hofmann will not talk about the attempt, but prison officials said they have no reason to believe the documents forger is still suicidal.The Utah Department of Corrections released a statement Wednesday at the conclusion of its investigation into Hofmann's overdose of anti-depressant drugs.

A sufficient number of the tricyclic sedatives were purchased from other prisoners to have caused Hofmann's death. But toxicologists were unable to determine how many of the pills he took, the statement said.

Hofmann's suicide attempt occurred about one month after his wife filed for divorce, but his attorney said the filing had been expected by Hofmann.

Earlier, authorities said they had found that letters by Hofmann had contained coded information about documents examiner George Throckmorton and two Board of Pardons members who at the beginning of the year had said Hofmann would spend the rest of his life in prison.

On Sept. 15, Hofmann's cell mate returned to his cell to find the confessed bomber comatose. He was rushed to University Hospital in critical condition and treated for an overdose. In addition, he suffered tissue damage to his right arm, apparently caused by laying lying on top of it for a long time.

Twelve days after the incident, Hofmann returned to the Utah State Prison.

Hofmann is now under normal surveillance at the prison. "We have no evidence to indicate he is suicidal," said spokesman Juan Benavidez.

Benavidez said Hofmann was not undergoing counseling or psychiatric care.

Following a plea bargain, Hofmann admitted to killing two people with pipe bombs to prevent disclosure of his document forgeries.