ORLANDO, FLORIDA — The Orlando gunman who killed 49 people on Sunday had been the subject of an FBI investigation for 10 months, but was not arrested due to lack of evidence.

The New York Times reports that in 2013, Omar Mateen made inflammatory remarks to his co workers at a security firm, claiming to be affiliated with terrorist groups like Al Qaeda and Hezbollah.

They reported him to the FBI, which put his name on the terror watchlist and began investigating his personal and financial records. The agency sent in an undercover informant and wiretapped his conversations.

They eventually sought help from Saudi intelligence officials to determine if Mateen had contacted any terrorists during his umrah pilgrimages to Mecca in 2011 and 2012.

FBI agents interviewed him twice. During this time, Mateen admitted to making the remarks to his coworkers, but claimed they were made in anger after his religion was ridiculed. Without sufficient evidence to pursue a criminal case, the investigation was closed and his name dropped from the watchlist.

Just two months later, in July 2014, he once again caught the attention of the agency, which uncovered his ties to a Florida-born suicide bomber in Syria. He was interrogated, but agents later determined the connection was not significant.

Mateen’s case may raise questions about the FBI’s ability to intercept terror threats. But even on the watchlist, the 29-year-old would have still been able to legally buy guns.

A bill aiming to stop suspected terrorists from legally purchasing guns was proposed but eventually rejected by the U.S. Senate last December, according to MSNBC.