LONDON - The 26-year-old US military veteran, suspected of shooting five people dead at Fort Lauderdale airport in the United States, told agents that US intelligence had infiltrated his mind and were forcing him to watch ISIS propaganda videos, according to CBS.

Gunman Esteban Santiago - an Iraq war veteran - opened fire in the baggage claim area at the Fort Lauderdale-Hollywood International Airport on Friday. He surrendered himself to the law enforcement, after having run out of ammunition, the Mail Online reported.

According to CBS, FBI confirmed in Nov 2016 that Santiago walked into an FBI office in Anchorage, Alaska and claimed his mind was being controlled by a US intelligence agency and that he was being forced to watch videos for Daesh.

Santiago's relatives said the 26-year-old had a history of mental health issues - some of which followed his military service in Iraq several years ago.

He served from 2007 to 2016 in the Puerto Rico National Guard and Alaska National Guard including a deployment to Iraq from 2010 to 2011. He received half a dozen medals before receiving a general discharge for unsatisfactory performance in August last year.

His aunt Maria Ruiz told NorthJersey.com that Santiago had returned from Iraq acting strangely but had seemed happy after the birth of his child in September last year.

But she said something happened to him about a month ago and he was hospitalized for two weeks. She did not have details of his condition.

'Like a month ago, it was like he lost his mind. He said he saw things,' she said.

Santiago's brother Bryan Santiago said he could have suffered a 'flashback' from his time in Iraq, despite never being diagnosed with PTSD, NBC reports.

Police are investigating whether the suspect was mentally disturbed or if he had links to Daesh, after he executed five people in the baggage claim hall with a gun he had checked in his luggage.