Gunman known to FBI,

WASHINGTON Since at least 2007, the FBI has been able to recognize the voice of Elton Simpson — one of the men suspected in the Texas shootings outside a contest featuring cartoons of the Muslim Prophet Muhammad.

Agents recorded the young man from Phoenix talking about fighting non-believers for Allah. About plans to travel to South Africa and link up with “brothers” in Somalia. About using school as a cover story for travelling overseas.

Simpson was arrested in 2010, one day before authorities say he planned to leave for South Africa. But despite more than 1,500 hours of recorded conversations, the government prosecuted him on only one minor charge — lying to a federal agent. Years spent investigating Simpson for terrorism ties resulted in three years of probation and $600 in fines and court fees.

Then, on Sunday, two men whom authorities identified as Simpson and Nadir Soofi opened fire in a Dallas suburb on a security officer stationed outside the contest. The officials spoke only on condition of anonymity.

The deliberately provocative contest had been expected to draw outrage from the Muslim community. According to mainstream Islamic tradition, any physical depiction of the Prophet Muhammad — even a respectful one — is considered blasphemous, and drawings similar to those featured at the Texas event have sparked violence around the world.

Simpson and Soofi were wearing body armour, and one shot the guard in the leg. A police officer returned fire and struck both men, killing them. The guard was treated for his injury at a hospital and released.

Simpson, described as quiet and devout, had been on the radar of law enforcement because of his social media presence, but authorities did not have an indication that he was plotting an attack, said one federal official familiar with the investigation. Less was known about Soofi who appeared to have never been prosecuted in federal court, according to a search of court records.

Simpson had worshipped at the Islamic Community Center of Phoenix for about a decade, but he quit showing up over the past two or three months, the president of the mosque said.

A convert to Islam, Simpson first attracted the FBI’s attention in 2006 because of his ties to Hassan Abu Jihaad, a former U.S. Navy sailor who had been arrested in Phoenix and was ultimately convicted of terrorism-related charges, according to court records. Jihaad was accused of leaking details about his ship’s movements to operators of a website in London that openly espoused violent jihad against the U.S.

In the fall of that year, the FBI asked one of its informants, Dabla Deng, a Sudanese immigrant, to befriend Simpson and ask for advice about Islam. Deng had been working as an FBI informant since 2005 and was instructed to tell Simpson he was a recent convert to the religion.

On Monday, federal agents spent hours at a Phoenix apartment complex where the men apparently lived. Bob Kieckhaver, one of a number of residents who were evacuated for about nine hours from units near the men’s apartment, said one of them had a beard and wore an Islamic version of a prayer cap.

“I’ve never seen him angry,” Usama Shami, president of the Islamic Community Center of Phoenix, said of Simpson. “That’s the honest truth. He was always having a grin.”