The Tarrant County district attorney’s office admitted Thursday that it withheld favorable evidence in the case of Michael Roy Toney, who was convicted of killing three people with a bomb on Thanksgiving Day in 1985.

Lawyers on both sides said they now expect Mr. Toney to be granted a new trial. He has been on death row since 1999.

“I want a new trial so that the truth can be exposed,” Mr. Toney said in an e-mailed statement distributed by supporters. “I need for my children, grandchildren and remaining family to know that I have been wronged and that I am innocent.”

Debra Windsor, a Tarrant County assistant district attorney, said prosecutors still believe Mr. Toney is guilty, despite their admission that “we failed to turn over documents we should have turned over.”

The bomb killed Joe Blount, 44; his daughter, Angela Blount, 15; and a visiting relative, Michael Columbus, 18. It had been packed into a briefcase and left on the steps of Mr. Blount’s trailer at the Hilltop Mobile Home Park, near Lake Worth.

Police never established a motive for the killings and finally came to believe the bomb was meant for someone else.

The crime remained unsolved for 12 years. Then Mr. Toney, in jail on an unrelated charge, told another inmate about it. The inmate informed authorities. Mr. Toney later said he was only engaging in a ruse to help the other inmate get out of jail.

No physical evidence connected Mr. Toney to the crime. But his ex-wife and his former best friend both testified that they had seen Mr. Toney with a briefcase near the mobile home park on the night of the bombing.

The best friend, Chris Meeks, has since recanted, and then un-recanted, his testimony. The ex-wife, Kim Toney, has stuck to her story, but has admitted to memory loss caused by military service in the Persian Gulf War.

Defense attorneys say the documents that the district attorney failed to produce show that prosecutors were aware of inconsistencies in the stories of Ms. Toney and Mr. Meeks.

“And those were the only two witnesses tying Michael to the crime,” said Jared Tyler, a lawyer for the Texas Innocence Network.

Mr. Tyler and Ms. Windsor jointly filed “agreed proposed findings of fact” with state District Judge Everett Young.

“The State failed to turn over to the defense no less than 14 documents containing exculpatory or impeaching evidence,” the proposed findings said. “Those documents included evidence of prior inconsistent statements of trial witnesses.”

Judge Young, who presided over Mr. Toney’s trial, now must rule on the findings. The case then goes back to the Court of Criminal Appeals, which could overturn Mr. Toney’s conviction.