(CNN) Shortly before imposing sentence on a convicted terrorist who managed to become a US citizen, a federal judge in Los Angeles on Friday directed two questions at the prosecutor in the case:

How did Vallmoe Shqaire get into the country in the first place? And what took the government so long to prosecute him once his terrorist past had been discovered?

The questions by US District Court Judge John F. Walter echoed those raised in a CNN report published Thursday detailing how Shqaire was made a US citizen in 2008 despite having served time in an Israeli prison for attempting to blow up a bus.

Assistant US Attorney Annamartine Salick acknowledged that Shqaire, 51, had "slipped through the cracks" of the immigration vetting system.

She said the state of information-sharing between countries back then was "not as advanced as we are today."

"We've come a long way," she added.

Once Shqaire became a citizen, legal protections afforded by the US Constitution kicked in, making it "an extremely difficult process" to prove that he had lied to obtain his citizenship, Salick told the judge.

Shqaire and an accomplice attempted to blow up a bus in Israel in 1988, according to court records. They did so at the direction of a cell of the Palestine Liberation Organization -- at the time, a terrorist group in the eyes of the US government. Shqaire was convicted and served four years in an Israeli prison for the attack, in which no one was hurt.

He failed to disclose his arrest, conviction or ties to the PLO at various stages of his years-long quest to become an American. His past crimes and his association with the group at that time, if known would have excluded him from becoming a citizen, authorities said.

According to court records, Shqaire was recruited by the PLO in the mid-1980s. He confessed to the bombing charge, and to assaulting fellow Palestinians suspected of collaborating with the Israelis. He claimed in court records decades later, after his terrorism conviction was discovered by the US, that his confessions were coerced by the Israelis following beatings and being confined to a tiny cell in which he could not stand up for weeks. US prosecutors said there were unaware of any evidence to support those claims.

Shqaire was charged in September with illegally obtaining his citizenship by omitting those facts from US immigration officials.

Salick acknowledged that authorities had a "source report" in 2010 in which Shqaire had allegedly boasted of serving time in prison in Israel. But, "at that time, we didn't have sufficient evidence," she said.

She described working nights and weekends on the phone with officials in Israel who were retrieving water-logged records in an effort to provide the US with documentary proof of Shqaire's crimes. The process took years.

Judge Walter made clear that his frustration was with that process, not Salick herself, whom he described as an "outstanding" prosecutor who did "an excellent job representing the government."

But the judge said he failed to understand why, if Shqaire truly posed a threat to the US, somebody "didn't get on a plane," to Israel, get the documents and, "get him out of here."

He said the delay undercut the notion that Shqaire posed a continuing threat.

Shqaire's defense attorney, Mark Werksman, asked the judge for a sentence of probation, noting his client's "peaceful" existence in the United States for two decades. The lawyer noted that he worked as a parking valet.

"He didn't try to start a sleeper cell for al Qaeda," the former prosecutor quipped.

Shqaire, wearing black slacks and a white dress shirt, spoke briefly on his own behalf.

"I am very, very sorry for what I have done," he said. "I love this country."

Walter said he found Shqaire's past acts in Israel "despicable," but that he did not view him as a terrorist as he stood before him three decades later.

He sentenced him to nine months in federal prison.

Immigration officials have already begun administrative proceedings to strip Shqaire of his citizenship. As part of his plea agreement with the government, Shqaire will be deported to Jordan following his release from prison.

Walter gave Shqaire until May 28 to surrender to begin serving his sentence.