Washington, June 10 (IANS): The US state of Missouri has executed Richard Strong, a 48-year-old Afro-American, for murdering his girlfriend and her two-year-old daughter in 2000, Efe news agency reported.

Strong was declared dead at 6.58 p.m. on Tuesday after being administered a pentobarbital lethal injection in the state prison in Bonne Terre, according to the Missouri Department of Corrections.

On October 23, 2000, Strong used a butcher knife to murder his then girlfriend Eva Washington and her two-year-old daughter, Zandrea Thomas, whom she had from a previous relationship.

According to the autopsy, Washington was stabbed 21 times and Thomas 12.

The police arrested Strong in his apartment and along with the two bodies they also found a three-month-old baby that Strong had with Washington.

Alyshia Strong, now 14, appealed on Monday to Governor of Missouri Jay Nixon to suspend the execution of her father, whom she has forgiven.

"He's always been with me, he's the only surviving parent I have, and I struggle in life. To see my father live would help me," Alyshia said recently in an interview.

Nixon rejected the clemency petition on grounds that the murders of Washington and Thomas were "were very brutal".

Strong's lawyers made a last-minute appeal before the Supreme Court, claiming that the execution of a mentally ill prisoner infringes the constitution but the judge refused to intervene.

Strong became the fourth prisoner to be executed in Missouri this year and the 16th in the country.