(CNN) -- Dutch authorities have joined the FBI in conducting criminal investigations into the discovery of needles in six sandwiches aboard four Delta Air Lines flights from Amsterdam to the United States, a military police spokesman in the Netherlands said Tuesday.
One person was injured when he bit into a sandwich containing a needle, Delta and Dutch officials said.
That passenger, James Tonjes, said he thought the object was a toothpick at first.
"When I pulled it out, then I found out it was a needle," he said Tuesday.
Delta: Needles found in sandwiches
Tonjes said he has been placed on medication to prevent HIV.
A second passenger aboard the same flight, Jack Drogt, told ABC's "Good Morning America" on Tuesday that he not only found a needle, he discovered after landing that his son also found a one in his sandwich aboard another flight from Amsterdam.
Unsavory truths about airplane food
The objects were discovered in the sandwiches as the planes were flying Sunday from Schiphol Airport in the Netherlands to Minneapolis, Seattle and two flights to Atlanta, according to Delta spokeswoman Kristin Baur. Two of the needles were found by passengers, she said. An air marshal aboard another flight found a needle.
Officials initially reported that four needles had been found. Baur said the two additional needles reported Tuesday were not new incidents but a clarification of earlier information.
U.S. Customs and Border Protection issued a brief statement Tuesday saying it had seized at least one item of food containing a "foreign object" and turned it over to the FBI, which has said it is conducting a criminal investigation.
On Tuesday, Robert van Kapel, spokesman for the military police in Schiphol, said detectives there were looking into who put the needles into the sandwiches and why. Military police provide police services at civilian airports in the Netherlands, according to the Defense Ministry.
Gate Gourmet, which provided prepared sandwiches to Delta, said the sandwiches originated at the firm's facility in Amsterdam. The company has been in business since 1992.
"This is a terribly upsetting situation," Gate Gourmet spokeswoman Christina Ulosevich said. "First and foremost is the safety of the traveling public. There's nothing more important to us at all than the safety of the passengers and crews."
Tonjes said it was about an hour before the flight was scheduled to land in Minneapolis when the flight crew served him a turkey and cheese sandwich.
He described the needle that punctured the roof of his mouth as being about an inch long. He said it looked like a sewing needle but did not have an eye.
"It happened so quick," he said. "I called the flight attendants, and they immediately took it. They didn't make an announcement, but they did go around and collect (the sandwiches)," he said.
FBI officials declined to comment Tuesday.
On Monday, Transportation Security Administration spokesman David Castelveter said the agency had notified all U.S. airlines with flights from Schiphol to the United States of the situation.
Castelveter told CNN Tuesday said the agency has developed catering security procedures for airlines and their contractors. TSA conducts inspections to ensure compliance, he said.
Delta is now serving sealed prepackaged food on these flights instead of the sandwiches, and no other needles have been found, said Baur, the Delta spokeswoman.
"Delta requires all its in-flight caterers to adhere to strict criteria in order to offer our customers the very best onboard meals," Baur said in a statement. "The safety and security of our passengers and crew is Delta's number one priority."
Ulosevich said Monday that Gate Gourmet provides food to other airlines but that it had not received any other reports of tampering.
"We are absolutely cooperating fully with federal and local authorities who are involved, and concurrent with that, we'll be conducting our own full-scale investigation."
Frequent flier Gary Leff, who rakes in more than 100,000 miles each year, said he's taking a "wait and see attitude" but isn't planning to change the way he thinks about airline food.
"I mean, this isn't going to be the first thing ever found in airline food and certainly not the first thing found in restaurant food," he said.
Leff is a frequent domestic flier for work and redeems his miles for international vacations, sharing his cheap travel expertise on his blog, View from the Wing.
He expects others to be bothered by this incident "for about 15 minutes," Leff said. He referenced a number of occasions when unwanted ingredients or objects have been discovered in foods and medicines over the past few decades -- incidents no one seems to worry about or even remember, he said.
"I think most people are just so happy to be served food in the sky that they'll forget it pretty quickly," he said.
Tom Fuentes, a former FBI assistant director, said he believes the incidents are "along the lines of a serious prank," rather than a terrorist act.
The discovery of needles does raise questions about oversight of off-site food preparation, where numerous people have access to food before containers are locked, he told CNN.
Among those questions, Fuentes said, are, "Who is watching the people who are preparing the food? What kind of background checks are they going through? What kind of security exists at those locations?"