Updated

The Latest on the pending execution of a Missouri man convicted of killing a woman and her two children in 1998 (all times local):

2:45 p.m.

Attorneys for a Missouri death row inmate have asked the U.S. Supreme Court to halt his execution.

Mark Christeson is scheduled for lethal injection Tuesday evening. The 37-year-old was convicted in the 1998 killings of Susan Brouk, her 12-year-old daughter and her 9-year-old son in Vichy, Missouri.

In the appeal to the nation's highest court, Christeson's attorneys cite concerns about the competency of his original trial court lawyers. They say the attorneys missed a 2005 deadline to file a federal court appeal, which is a standard procedure in death penalty cases.

Christeson was hours away from execution in 2014, when the U.S. Supreme Court stepped in and remanded the case, citing the missed deadline for a federal appeal.

If the court doesn't step in this time, Christeson's lethal injection would be Missouri's first execution since May.

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11:30 a.m.

A Missouri man convicted of killing a woman and her two children in 1998 is asking state and federal courts to spare his life a day before his scheduled execution.

Mark Christeson is set for lethal injection at 6 p.m. Tuesday. If carried out, the execution will be Missouri's first since May.

Among the issues raised in Christeson's pending court appeals is that his trial lawyers were so inept they missed a 2005 deadline for a federal appeal.

Christeson was 18 when he and a 17-year-old cousin attacked Susan Brouk at her rural home in Vichy, then killed Brouk, her 12-year-old daughter and her 9-year-old son.

The cousins were caught after fleeing to California. Christeson's cousin testified against Christeson and was sentenced to life in prison without parole.