Home Secretary Charles Clarke signed an order Friday authorizing the return of Neil Entwistle, 27, to Massachusetts. That cleared the last legal hurdle in Britain and Entwistle could be sent back at any time.
Entwistle, who was arrested in London on Thursday, wished to return to the United States "as soon as possible" to face the charges, his attorney Ben Brandon told a hearing earlier at Bow Street Magistrates Court.
District Judge Anthony Evans told Entwistle that his decision to voluntarily return would be irrevocable.
"Yes, that's right," Entwistle replied. He glanced briefly at his father, Cliff Entwistle, as he signed the form consenting to return.
"He was always inclined to consent," Judith Seddon, another lawyer representing Entwistle, told reporters outside court.
Entwistle could return to the United States very soon now, reports CBS News correspondent Vicki Barker (audio).
"He wants to cooperate with the authorities in any way that he can, and he is anxious that the delay may cause his late wife's family and his own additional distress, something he wishes to avoid," Seddon said. "He believes that he will receive a fair and a proper hearing in the U.S.A. of these very serious allegations."
Entwistle is accused of fatally shooting Rachel Entwistle, 27, and 9-month-old Lillian on Jan. 20.
"He's facing two counts of murder, one for his wife and daughter each. And one count of a firearm possession illegal and one count of illegal possession of ammunition," Middlesex District Attorney Martha Coakley
Coakley said forensic results indicated the .22-caliber handgun used in the killings was from a collection owned by Entwistle's father-in-law. Prosecutors believe Entwistle took the gun from his father-in-law's home, then secretly returned it after the slayings.
Authorities allege Entwistle shot his wife in the head and his daughter in the abdomen as they lay together in bed. The district attorney said it was unclear whether the two were awake or sleeping at the time, but said it may have been intended originally as a murder-suicide, with Entwistle changing his mind at the last moment.
It didn't seem "a conventional domestic violence fight, heat of passion kind of crime scene. It also, however, doesn't indicate someone who had this well planned," Coakley told The Early Show co-anchor Julie Chen.
In Massachusetts on Friday, newly released court documents alleged that Entwistle told police three days after the slayings that he did not kill his wife and daughter, but discovered their bodies and then contemplated suicide.