Asked what he was doing in New Zealand, he replied: "I'm visiting a friend.''
He said the Immigration officer then asked: "Is it Kim Dotcom?''
"When I said 'yes', she started getting very inquisitive.''
Leitch said he was quizzed about why he had bought his ticket the same day he travelled and why he had returned to New Zealand just six weeks after his last visit.
Leitch said he believed his arrival card was marked in a way which identified him to a Customs officer, who also grilled him before leaving the airport.
"The search happened because of that... because I gave Kim Dotcom's address.''
He said he had intended staying just a few days so arrived with an overnight bag and clothes for the short visit. He said he also had a work bag containing a laptop, diary and notebooks. In spite of this, it took more than an hour for the Customs official to carry out a search.
Leitch said he was asked to open his computer bag, then his laptop and enter his password.
"There were a lot of emails regarding the trip. He was looking at all the subject lines... everything they were doing was being logged in their computer system. I asked what he was doing. He said he was taking notes.''
Leitch said the Customs officer then began to go through Leitch's diary and notebooks.
"The Customs agent kept leaving and going over to talking to his supervisor. I was starting to get kind of nervous. I have no idea what they are looking for.''
Leitch had brought a shirt he had printed with the words "Free Kim Dotcom'' on the front.
He said the Customs officer held it up and asked: "What's this?''
The questioning heightened Leitch's concern. "I wanted to keep Kim's spirits up. I said it was a shirt I made for Kim... it's just a joke.''
The search continued with the officer searching each piece of clothing.
At one stage, Leitch said he asked if the search would affect his next visit to New Zealand. "He said `it might or it might not'.''
Leitch said the decision to focus on him because of the Dotcom link was bizarre.
"It is a really interesting story from a journalist's perspective. I don't work for Dotcom, I'm not an employee.''
He said he was also left uncomfortable about the information collected about him and what it might be used for.
"It is not New Zealand's fight. It is not the Customs gentleman's fight. It is strange in a country known to be open and friendly.''