This August 2016 image shows Abdul Razak Ali Artan in Columbus, Ohio on the first day of classes. (Kevin Stankiewicz/ via AP)

The Ohio State University student who used his car and a knife to attack a group of people on campus last month should have received more thorough vetting when his family was seeking refu­gee status in the U.S. years earlier, the chairman of the Senate Judiciary Committee alleged Thursday.

When the mother of Abdul Razak Ali Artan asserted in 2013 that she needed to flee to the U.S. because she feared persecution from “Militia and Al-Shabbah,” it should have triggered more questioning of her older children, including Artan, Sen. Charles E. Grassley (R-Iowa) wrote in a letter to Homeland Security Secretary Jeh Johnson.

Grassley wrote that such questioning did not seem to have happened, at least according to the records his committee obtained via a whistleblower.

“Further questioning could have eliminated the possibility that the asylees had dubious ties to the terrorist group and could have allowed for more robust vetting and data collection,” Grassley wrote. “However, although common in these cases, no additional questioning was conducted.”

“Al-Shabbah” likely refers to al-Shabab, an al-Qaeda linked terror group active in Somalia. That is Artan and his family’s home country, though authorities have said previously they came to the U.S. as Somali refugees via Pakistan.

Grassley wrote that Artan came to the U.S. with his mother, Fatima Abdullahi, and six siblings, and that Abdullahi said her husband had been kidnapped and that her children would be kidnapped and recruited by “Al-Shabbah” if they remained in Somalia.

The Department of Homeland Security did not immediately respond to a request for comment. A State Department spokeswoman referred questions to that agency, which administers the refu­gee screening process.

Artan, believed to be 20, was shot and killed by a police officer after he drove a car into a crowd on Ohio State’s campus, then emerged and slashed bystanders with a knife. Authorities have said Artan, a Muslim, is believed to have radicalized online and that he was inspired by radical cleric Anwar al-Awlaki and the Islamic State, though he apparently had no actual ties to terrorists overseas.

Eleven people were injured in Artan’s attack, which was initially broadcast as an active shooter and sparked fears across the college campus.

The vetting of refugees has been a hot-button political issue, with President-elect Donald Trump and others suggesting that if the United States welcomes such people, especially from Syria, it raises the possibility of terrorist attacks. Trump has said Syrian refugees represent a “great Trojan horse,” and he has called for a ban on Muslim immigration or “extreme vetting” of immigrants.

The government already has a screening process — which FBI Director James B. Comey said has “improved dramatically” — though even he acknowledged that there could be some problems with checking those coming from Syria.

“I can’t sit here and offer anybody an absolute assurance that there’s no risk associated with this,” he said at a congressional hearing last year.

Even if Artan was questioned more extensively three years earlier, it is unclear if that would have prevented him or his family from coming into the country. Grassley wrote that the Judiciary Committee had obtained some records about the matter, though he asked Johnson for even more. U.S. Rep. Adam B. Schiff (D-Calif.), who was briefed by law enforcement officials on the case, has said previously that Artan’s family members had not noticed any signs of radicalization.

“Either he kept it very quiet or there was something that moved him very quickly from being a consumer of radical propaganda to acting out violently,” Schiff has said.

Artan graduated from a local community college in Columbus before transferring to Ohio State as a junior this semester; he told a student journalist on the first day of classes in August that he was worried about Trump’s anti-Muslim rhetoric and said he was concerned about praying in public at the large school.

A representative for Grassley said the committee is researching whether it can publicly release the records it already has received. Artan’s family has not spoken publicly, and efforts to contact them since the attack have been unsuccessful.

In addition to possibly inadequate questioning, Grassley wrote that the records his office had obtained bore the name “Immigration and Naturalization Service,” an indication they might be out of date, as that name was replaced in 2013. He wrote it was unclear whether that meant the review was conducted according to older standards, or whether the name on the form had simply not been updated.