TUCSON, Ariz. — Devastated by the death of his only daughter in the bloody ambush on Rep. Gabrielle Giffords, John Green — son of former Mets manager Dallas Green — today lashed out at the crackpot killer.

“I think they should execute him,” said a broken-hearted John Green, whose 9-year-old child Christina-Taylor was fatally shot when crazed gunman Jared Loughner, 22, opened fire at a political meet-and-greet hosted by Giffords yesterday.

Giffords was critically wounded in the attack; Christina and five others at the event were killed.

Green, who works as a scout for the LA Dodgers, said dad Dallas Green and mom Sylvia Green were still on a holiday vacation when they first heard of the ambush on television — unaware their own beloved granddaughter was among those killed in the bloodbath.

“She didn’t know what was going on in Tucson,” Green said of his mom, but “She had a premonition,” and called him.

“I broke down on the phone and told her,” he said. “It was hard to tell her that Christina had been killed. She also broke down and she couldn’t talk anymore.”

Today, Dallas and Sylvia Green are making their sad journey to Tucson to be with the family, he said.

The devastation has been overwhelming, John Green told The Post, unable to hold back tears.

“She was born on 9/11, so when you look at the bookends of her life, they were pretty tragic,” he said. “But everything in the middle was the best.”

Green said the little girl’s 11-year-old brother, also named Dallas after his granddad, was at karate school with mom Roxanna Green.

John Green said he was cleaning up a house they were going to rent out.

Meanwhile, Christina went with family friend Susan Hileman to the Giffords congressional event in front of a local Safeway.

When Loughner opened fire, Christina and Hileman were practically standing next to Giffords, Green said.

“She was at the wrong place at the wrong time,” he said. “But I’m still very angry. I’m very angry that someone would choose that venue to take out their anger. It is a cowardly way to handle their grievances

” My wife is very forgiving, but I’m not.”

Green said doctors told him the bullet entered Christina’s back and exited out of her left chest area.

He said his little girl became interested in politics during the last presidential election — and was not just “very personable,” but very “persistent.”

“When she sets her mind to something, she gets it done,” he said.

He said Hileman knew of Christina’s interest and took her along to the Giffords meet-and-greet.

Retired Col. Bill Badger — who also showed up at the political event — told The Post that he noticed the youngster, and her beaming, wide smile.

“It looked like she was having the time of her life,” he said.

Badger said the child was standing directly next to and a little behind Rep. Giffords when the ambush unfolded.

Green said his first idea of the horror that unfolded at the event came after his wife — who was alerted by Hileman’s husband, Wilson — called him.

“My wife called and said there was an accident, but I thought it was a car accident — I didn’t know that it pertained to my daughter,” he said.

But at the hospital, “That’s when I saw her clothes were everywhere, and that’s when I had a feeling of dread.”

The grieving dad his daughter loved baseball, dancing, swimming and horseback riding.

He feels nothing but disgust for the shooter who ended her life.

“It would be a waste of millions of dollars” to keep him alive, he said.

“They should use the money to help kids in school instead of some idiot.”

Tears rolling down his face, Green said he will always keep his favorite image of his daughter in his heart.

“I remember the way she would come up to me in the morning and say, ‘Daddy, daddy! It’s time to get up!’” he said. “It was the way that she would say it and she would put her cheek on my cheek.”