Federal agents are investigating if four men from Minnesota were trying to reach Syria to join ISIS last year while they charged one of them with repeatedly lying to the FBI, prosecutors said Thursday. Somali-American Hamza Ahmed, 19, had claimed he did not know the other men and allegedly lied about his travel plans.

While Ahmed was taken into custody Thursday morning until a detention hearing is held on Monday, the other three have still not been arrested, Star Tribune reported. The four had reportedly traveled together in a bus to John F. Kennedy International Airport in New York City to board outbound flights in November. Ahmed and another man, identified only as M.F., were booked on a flight to Istanbul, Turkey, which is known to have been a gateway to Syria. The other two men, identified as H.M.M. and Z.A., were traveling to Athens via Moscow.

By the time the federal customs and border agents recognized Ahmed as suspicious, he had already boarded his flight. But authorities managed to pull him from the plane, minutes before takeoff, Star Tribune reported. He was interviewed in New York and later in Minnesota, where he told the agents he was traveling alone and did not know the other men, Reuters reported.

Investigators found Ahmed’s itinerary suspicious and said he lied about spending four days in Spain on vacation. Investigators said, according to CBS Minnesota, that he would have just spent one day in Madrid, without a hotel room.

Ahmed had also claimed that he bought the ticket with his own money and did not know M.F. However, surveillance camera footage had showed the four men arriving at the Minneapolis bus station in the same car, checking in their luggage, waiting and boarding the bus together, NBC News reported. The other three men were also stopped from boarding their flights at JFK and investigators are probing whether the men planned to join ISIS in Syria.

FBI officials are also investigating if there was a link between Ahmed and another man, identified as H.A.M., who had reportedly traveled to Syria earlier in 2014, the Star Tribune reported. Agents had found a series of exchanges between the two men on Twitter, where they had also allegedly decided to meet at a mosque and find a place to talk.